Waste Water Tank Size?

[skyhawk]

For you and YOUR situation...the type of cruising you do....
What do YOU consider to be a minimum tank size for black and grey water, and why?

I'm interested in all perspectives I suppose, but especially from folks who anchor out, coastal cruise where you might stay in little town anchorages or docks for a few days or weeks playing tourist, etc...

I was daydreaming the other day looking at various specs for a few different makes and models.
Something caught my eye while on the Nordhavn site...comparing the
52 with 120Gal/110gal tanks
to the new 475 with only 50 gal/50gal
Now I know these boats are quite the same size, but I'd argue that they're in the same ballpark...and 50 gallons strikes me a quite small...and such a big difference from the 52!

Coming from the RV world, my small motorhome has something on the order of 30 gallon black and grey tanks and my grey tank is quite a limitation!

 

[rslifkin]

Most of us don't have grey water tanks at all. There are very, very few places in the world where they're required for recreational use. On my boat, I've got a 70 gallon black tank, no grey tank.



How big a black water tank you need depends on where you cruise. Offshore, you don't really need the tank at all. For coastal and inshore, you'll use it, but size just determines how often you'll have to find a pumpout. I personally find my 70 gallon tank plenty large. With 2 of us on board, it's good for anywhere from 7 - 10 days before I'm looking for a pumpout.

 

[tiltrider1]

40 gallons gives me two weeks between pump outs for two people full time on the boat. I use vacuflush toilets. No grey water.

 

[Portage_Bay]

If you want to capture grey water and never discharge overboard then the tank needs to equal your potable water capacity. If you have a watermaker you're gonna need a BIG tank.

 

[O C Diver]

I have an 80 gallon black water tank which I feel is good for a 2 stateroom boat. I tend to cruise solo and find that the 300 gallons of freshwater will need to be replenished before the waste tank needs emptying, so do both when cruising. As an interesting side note, the grey water from the bathrooms and galley can be directed to the holding tank. Have only needed this at Isle Royale in Lake Superior, but it was very nice to have the ability.

Ted

 

[Woodland Hills]

We have 375 gal of freshwater and 275 gal of black water. It works for us.....

 

[Shifty]

250 fresh, plus a water maker. 65 black with fresh water flush. Good for a week with four of us. We have a small gray water tank for the shower that helps break down suds before they go overboard.

 

[slowgoesit]

480 gallons of fresh, two holding tanks, 204 gallons each. Grey can be directed to holding tank if needed.

 

[SteveK]

We have 375 gal of freshwater and 275 gal of black water. It works for us.....

Is that freshwater flush. Just curious as I agree you have it covered.

 

[Comodave]

I agree that 50 gallons for a black water tank is too small. We have 45 and I would love to have twice that but there isn’t room.

 

[rsn48]

So someone has to be the odd man out. For my black water tank, I have............... 0.

I have an Airhead composting toilet. I got rid of my traditional Jabsco head which pumped directly into the salt chuck - old boat. I'm a big fan of "Gone with the Wynn's" and started watching them when they were in their large motorhome full timing it. They got rid of their conventional RV toilet and installed a composting toilet instead. Most folks have a hard time with this concept but the composting toilet has no smell. The large area for the poo and sphagnum moss or coconut coir is vented to the outside and has a full time fan.

The theory is simple. When you do your thing in an outhouse, we all know it reeks. The reason for the smell is a chemistry I can't tell you as I don't know, but the combination of urine with feces grows the smell. If you can keep your pee separate from the pooh there is no smell. Once the pooh hits the coconut coir and you are "done," then you crank the whole shebang approximately 5 times with a crank to ensue everything is mixed together.

The coconut coir acts as a desiccant removing moisture from the pooh which is then vented to the outside. A composting toilet is not a composting toilet, we have been lied to, surprise surprise. A composting toilet is really a desiccant toilet, drying everything out. It takes about a year for everything in the coconut coir to compost.

The main compartment for pooh holds about a month if you only add toilet paper for pooing and not peeing. The toilet paper for peeing goes in a separate small garbage can.

For peeing both men and women sit down as there are two holes directly below the sexually appropriate equipment and the holes direct the pee into a separate container. One container holds about 2 1/2 gallons, usually people have two containers. The pee gets dumped over the side, many put it down their head sink so as not to enrage others. The pooh is put in a composting bag and can be added to composting piles that will be used in flower and shrubbery areas, but not vegetable gardens.

But with the Airhead I can go roughly a month before the coconut coir and assembled chorus are thrown out. So my entire "holding" tank is for pee only and it is 5 gallons strong.

Also my water tank is 40 gallons. I don't use any water for flushing. The water I use is only for washing dishes, done once a day to save water and for cleaning. I bring bottled water along for consumption in flats. So my daily consumption of water from my holding tank is less than one gallon a day.

Instead of a black water holding tank, I tore out my old fuel tanks and added two large newer ones - instead of 100 gallons, now the boat has 160 gallons.

 

[boomerang]

So someone has to be the odd man out. For my black water tank, I have............... 0.

I have an Airhead composting toilet. I got rid of my traditional Jabsco head which pumped directly into the salt chuck - old boat. I'm a big fan of "Gone with the Wynn's" and started watching them when they were in their large motorhome full timing it. They got rid of their conventional RV toilet and installed a composting toilet instead. Most folks have a hard time with this concept but the composting toilet has no smell. The large area for the poo and sphagnum moss or coconut coir is vented to the outside and has a full time fan.

The theory is simple. When you do your thing in an outhouse, we all know it reeks. The reason for the smell is a chemistry I can't tell you as I don't know, but the combination of urine with feces grows the smell. If you can keep your pee separate from the pooh there is no smell. Once the pooh hits the coconut coir and you are "done," then you crank the whole shebang approximately 5 times with a crank to ensue everything is mixed together.

The coconut coir acts as a desiccant removing moisture from the pooh which is then vented to the outside. A composting toilet is not a composting toilet, we have been lied to, surprise surprise. A composting toilet is really a desiccant toilet, drying everything out. It takes about a year for everything in the coconut coir to compost.

The main compartment for pooh holds about a month if you only add toilet paper for pooing and not peeing. The toilet paper for peeing goes in a separate small garbage can.

For peeing both men and women sit down as there are two holes directly below the sexually appropriate equipment and the holes direct the pee into a separate container. One container holds about 2 1/2 gallons, usually people have two containers. The pee gets dumped over the side, many put it down their head sink so as not to enrage others. The pooh is put in a composting bag and can be added to composting piles that will be used in flower and shrubbery areas, but not vegetable gardens.

But with the Airhead I can go roughly a month before the coconut coir and assembled chorus are thrown out. So my entire "holding" tank is for pee only and it is 5 gallons strong.

Also my water tank is 40 gallons. I don't use any water for flushing. The water I use is only for washing dishes, done once a day to save water and for cleaning. I bring bottled water along for consumption in flats. So my daily consumption of water from my holding tank is less than one gallon a day.

Instead of a black water holding tank, I tore out my old fuel tanks and added two large newer ones - instead of 100 gallons, now the boat has 160 gallons.

I just can't get on the composting head bandwagon. Like you, our boat is smaller & storage comes at a premium. We're always looking for ways to cram stuff into unused/wasted space and for ways to make more space. If we had a large, dedicated holding tank, which we don't, since we have a head with a built-in tank that the bowl sits atop...a glorified RV head as Peggy calls it...yes, the first instinct would be to pull it out to make more stowage room for something else and put a Natures head thing in. But then you need to store a bail of coconut mulch stuff somewhere so how much room have you gained? Strike 2 for me is, as a guy-and maybe it's just a personal plumbing defect, I don't pee too well sitting down! This is way TMI but personally ,after doing my #2 business, I stand up, turn around and more completely void my bladder. Like I said, TMI unless everyone reading this thread happens to be a uroligist. Strike 3 for the coconut system is there's no way my wife is going to allow any pee to be poured down the sink where she brushes her teeth and washes her face! Hell, I'm a dude & I'll happily pee anywhere that I can get away with but I'm pretty sure I'll have to draw the line at using the sink!

 

[FF]

For the new build or other folks with the space , remember a std RV toilet (gravity drop to the holding tank directly below) requires 1/5 to 1/10 the usual capacity for black water.


Or will usually go 10X the time before needing to be emptied.

 

[High Wire]

Our waste tank is 35 gallons. 7-10 days fills it to about 3/4 if we are full time cruising. We generally time our pumpout with a fuel top off once a week or so.

 

[rslifkin]

For those mentioning fresh water capacity, I've got an irritatingly small 65 gallon tank. I'll always need to go in for fresh water before I've filled the 70 gallon black tank enough to be thinking about a pumpout.

For the new build or other folks with the space , remember a std RV toilet (gravity drop to the holding tank directly below) requires 1/5 to 1/10 the usual capacity for black water.


Or will usually go 10X the time before needing to be emptied.

That's why our forward head gets far more use than the aft. The forward head has a very short hose to the tank with a lot of drop. So while it's not quite to RV toilet levels, it doesn't take much water to clear the line. The aft has a longer run, so it needs a bigger flush.

 

[caltexflanc]

We lived aboard full time on our old Hatteras 56MY. Since we spent most of it at anchor or on a mooring, we loved having a 210 gallon holding tank.

I should note that at many east coast mooring fields, there is a pumpout boat available, and in several cases will come pump you out on a regular schedule whether you ask them or not.

If you do a fair amount of offshore cruising, holding tank size really isn't much of a limitation.

We have composting toilets at a rustic cabin on the California coast in a spot where septic is not allowed (too near a river). I don't like them and would never have one on a boat. Way too much hassle.

Having Vacuflush freshwater heads was great. We had a 350 gallon water tank with another 40 in the hot water heater. I eternally had a watermaker on The List, but could never get it to pencil out, even when having to pay for water in the islands.

 

[HeadMistress]

First, you need to know that USCG regs make it illegal to combine black and gray water in the same tank...there can't even be any common plumbing. So if you think you need to hold gray water, you'll need a separate gray water tank.


As for how big a black water tank, that depends on the amount of flush water your toilets use, how many people will be using them (fwiw, the avg adult uses the toilet 5x/24 hrs), how much you'd be dependent on pumpout facilities to empty it vs ability to dump at sea, whether treatment instead of holding is an option, and the impact 8.333 lbs/gal of weight (50 gals weighs 417 lbs + the weight of the tank) in the planned tank location will have on trim and other factors...and just how much sewage you really want to have to manage.


--Peggie

 

[Woodland Hills]

Is that freshwater flush. Just curious as I agree you have it covered.

Yes, freshwater flush. We do not bother clearing the line from toilet to tank so we don’t use much water. Here in Marathon we pumpout with a 50gal tank on a golf cart: we average about 1.5 tanks a week so we generate about 75 gals a week.

 

[skyhawk]

For the new build or other folks with the space , remember a std RV toilet (gravity drop to the holding tank directly below) requires 1/5 to 1/10 the usual capacity for black water.


Or will usually go 10X the time before needing to be emptied.

well that brings up a good point. Gallon for gallon I suppose they are different in terms of how much water is used in flushing
I started this thread coming from the perspective of the RV..... Having basically no experience with marine heads
are you saying that the marine heads use 5 to 10 times the water for flushing, compared to an RV head?...meaning that a 30 gallon RV tank would be equivalent to maybe 150 gallons or more on a boat? understand it uses more water to flush out the hose, but that seems like a lot more!

 

[OldDan1943]

My AT34 has about a 40gal blackwater tank. It will easily provide more than enough room, for 2, for a week. I had 4 people using it, had the tank pumped once a week with still room left over for more.
I carry 150gal FW, gray water, over the side.
I have a water making but have yet found a need to use it.

 

[skyhawk]

well that throws out the x5 to x10 thing
if got on the order of 30 gallons black in my RV, with 2 adults and three kids using it almost exclusively we can easily go more than 4 days.... don't think I've ever filled it up so I don't know for sure.....and my rv's bathroom sink goes to the black tank too.
Regardless, I know I'd want substantially more in a cruising boat.

 

[HeadMistress]

Fwiw, today's marine toilets use an average of .5 gal water/flush. Depending on where you plan to cruise--mostly coastal waters or internationally--a Type I MSD (treatment device) could reduce the need to use a tank and the ability to dump a tank in open sea can reduce the tank size needed considerably.



--Peggie

 

[rsn48]

But then you need to store a bail of coconut mulch stuff somewhere so how much room have you gained?

Don't know where you got the "bail" thing. Each "brick" is slightly smaller than a loaf of bread. One loaf will last roughly for one month of full time use. Below is a link to 4 blocks in a package. You will see one brick expands to 3 cubic feet (you lightly moisten the brick broken up with water).

https://www.homehardware.ca/en/5kg-...ISXZPB9S8sVEw2MxvKEaAsufEALw_wcB&gclsrc=aw.ds

I know most don't want a composting toilet I get it, but I'll provide some links for the curious. These videos are from the Wynn's RV vlog, they now live on a caterman, have for the last 4 1/2 years. They have grown to love their composting toilets so with the cat they bought, they turned one head into a composting head space. Their second head they left "traditional" for visiting guest. The discussion whether standing or sitting to pee for a man is even in the discussion.

Three thousand years ago when Jesus was in diapers, I worked at a large acute care hospital in Vancouver as an orderly to pay for my university degree. I was the guy who went around and drained catheter bags and emptied urinals. There are guys who have a very hard time peeing laying down in a hospital bed, they are just too brainwashed to adjust... lol.

Pee down the sink, you don't have to do that, you can just pour it over the side or walk it to a bathroom at the marina you are staying at and dumping it in the toilet. Probably less than 1 % of boats in my area have composting toilets, that estimate may even be high. But in Desolation Sound if there are two hundred boats in one anchorage (I exaggerate to make a point) it will be me and one other guy pouring pee off the back of the boat. If you don't want to piss of your neighbours off ... ha ha.. get it .... you can just pour the contents over the back or side at night. Its pooh in the water that is the real issue and you aren't doing that.

So here is my favourite RV now boating couple discussing composting toilets and the "issues" around it:

Why a composting toilet:

How to prep and dump a composting toilet:

 

[Matt]

“ The pee gets dumped over the side, many put it down their head sink so as not to enrage others.”

Sorry, but the idea of filling the sink’s P-Trap with pee is a no go for me... Yeah, of course you flush it with fresh water but still...

 

[skyhawk]

Fwiw, today's marine toilets use an average of .5 gal water/flush. Depending on where you plan to cruise--mostly coastal waters or internationally--a Type I MSD (treatment device) could reduce the need to use a tank and the ability to dump a tank in open sea can reduce the tank size needed considerably.



--Peggie

I have been reading your book. Haven't gotten all the way through yet. One thing I'm not yet clear on is where you can dump IF you have one of these treatment devices.

So, a half gallon flush. On average that is quite a bit more than an RV, where I suppose where we'll use next to nothing for most flushes and maybe a half for #2? Juyst a guess....Not sure about that

 

[OldDan1943]

“ The pee gets dumped over the side, many put it down their head sink so as not to enrage others.”

Sorry, but the idea of filling the sink’s P-Trap with pee is a no go for me... Yeah, of course you flush it with fresh water but still...

and no one ever pees in the shower.

 

[koliver]

“ The pee gets dumped over the side, many put it down their head sink so as not to enrage others.”

Sorry, but the idea of filling the sink’s P-Trap with pee is a no go for me... Yeah, of course you flush it with fresh water but still...

A P-Trap is a shore side phenomenon, required to keep sewer gasses in the sewer, and not in the bathroom. The hose from the drain goes directly down to the thru-hull, which is usually in the boot stripe. Listen while under way, you should hear the water lapping at the thru hull. If you don't hear anything, the thru hull is below the water line, but in both cases, a strait shot, no trap required.
But I agree that the sink is not for that.

 

[HeadMistress]

One thing I'm not yet clear on is where you can dump IF you have one of these treatment devices.

The discharge of TREATED waste is legal in all waters except specifically designated "NO discharge zones." You'll find a list of those here (and surprisingly the EPA keeps it up to date) EPA NDZ list by state. You'll find a basic description of how they work on page 11 in my book.



The discharge from a treatment device MUST go directly overboard...sending treatment to a holding tank will not make it legal to dump a tank anywhere inside the "3 mile limit." Reason: although the two most popular devices--the Raritan ElectroScan and their PuraSan--reduce bacteria count to less than 10/100 ml (the legal limit is 1000/100 ml), only one of the li'l buggers has to survive in a tank to quickly multiply into far more than the legal limit.


If you'd like to explore all your options in more detail than is practical in a forum discussion and can find the time to spend up to hour doing so on the phone, send me a PM so we can find a mutually convenient day/approx time to do that. I don't charge anything just to help people sort everything out and offer suggestions.


--Peggie

 

[ghost]

A P-Trap is a shore side phenomenon, required to keep sewer gasses in the sewer, and not in the bathroom. The hose from the drain goes directly down to the thru-hull, which is usually in the boot stripe. Listen while under way, you should hear the water lapping at the thru hull. If you don't hear anything, the thru hull is below the water line, but in both cases, a strait shot, no trap required.

But I agree that the sink is not for that.

If you are in my forward head and somebody forgot to put the drain plug into the empty sink, you will be frozen from the draft. I just replumbed my aft head and put a trap in, no draft. Going to retrofit my fwd head now and stop freezing.

 

[skyhawk]

One thing I'm not yet clear on is where you can dump IF you have one of these treatment devices.

The discharge of TREATED waste is legal in all waters except specifically designated "NO discharge zones." You'll find a list of those here (and surprisingly the EPA keeps it up to date) EPA NDZ list by state. You'll find a basic description of how they work on page 11 in my book.



The discharge from a treatment device MUST go directly overboard...sending treatment to a holding tank will not make it legal to dump a tank anywhere inside the "3 mile limit." Reason: although the two most popular devices--the Raritan ElectroScan and their PuraSan--reduce bacteria count to less than 10/100 ml (the legal limit is 1000/100 ml), only one of the li'l buggers has to survive in a tank to quickly multiply into far more than the legal limit.


If you'd like to explore all your options in more detail than is practical in a forum discussion and can find the time to spend up to hour doing so on the phone, send me a PM so we can find a mutually convenient day/approx time to do that. I don't charge anything just to help people sort everything out and offer suggestions.


--Peggie

Wow, thank you Peggie! That is very generous!!
I'm only in the very early dreaming stages to have any meaningful discussion on the matter...just wrapping my mind around the differences between this and RV life form a very high level.

So I just looked at Florida on that link you provided..just as an example because that's where I live.... not really many places. I'm suprised. Seems like a treatment device would be nice to have in a boat then!
Does that also include inland waters where the anchorages are?

I suppose I should put down my newly received copy of Voyaging Under Power & finish your book that I bought a few weeks ago!