Holding tank vent fitting options

[Comodave]

I believe that I used a 1 amp fuse on my Scad system. So it is really a low draw. And it was simple to install.

 

[HeadedToTexas]

The old float type sensor on our original tank level system was stuck most of the time, so I abandoned it and installed a Scad sensor. Simple to install and use and it has been extremely reliable.

The “vent as overflow” discussion was mostly to arrive at the conclusion that lowering the maximum level in my tank drops it from a 30 gallon tank to a 28 gallon tank. Both are quite small for our ambitions.

Instead of the simple, effective, and inexpensive Uniseal, what about glassing in an elbow and hose barb much like the manufacturer did for the other tank connections? That would be at least as secure a connection and seal, and prevent the protruding pipe thing from reducing the usable tank volume.

 

[rslifkin]

Instead of the simple, effective, and inexpensive Uniseal, what about glassing in an elbow and hose barb much like the manufacturer did for the other tank connections? That would be at least as secure a connection and seal, and prevent the protruding pipe thing from reducing the usable tank volume.

I see no problem with that. A uniseal is pretty much the only practical option for a plastic tank unless you have inside access to use a mushroom fitting, but for a fiberglass tank you can certainly glass a fitting into the tank.

 

[HeadMistress]

The "protruding" pipe need not extend more than 1/2" inch below the Uniseal.

If your existing tank fittings are in the end of your tank as they are on OEM and off-the-shelf tanks, you're already losing capacity because contents will overflow into the inlet line when the level reaches the bottom of that fitting and a pumpout will leave up to 2" in the bottom of the tank when the level falls to the top of the discharge fitting and begins to suck air. Relocating all the fittings to the top of the tank with a diptube on the discharge fitting that' long enough to touch the bottom of the tank and is cut at about a 25 degree angle (any flatter can trap TP and solid waste under it, any sharper leaves too much in the tank) allows you to use all of the stated (usable) capacity of the tank which is never every last cubic inch..

--Peggie

 

[CharlieO.]

The "protruding" pipe need not extend more than 1/2" inch below the Uniseal.

If your existing tank fittings are in the end of your tank as they are on OEM and off-the-shelf tanks, you're already losing capacity because contents will overflow into the inlet line when the level reaches the bottom of that fitting and a pumpout will leave up to 2" in the bottom of the tank when the level falls to the top of the discharge fitting and begins to suck air. Relocating all the fittings to the top of the tank with a diptube on the discharge fitting that' long enough to touch the bottom of the tank and is cut at about a 25 degree angle (any flatter can trap TP and solid waste under it, any sharper leaves too much in the tank) allows you to use all of the stated (usable) capacity of the tank which is never every last cubic inch..

--Peggie

Thanks for the info Peggy, this winter I plan on seeing if I can finagle my tank out and redo my vent line to a larger mushroom type. and I will check the discharge pipe also. Plan to replace all the waste lines also. Slowly working down my list but the waste smell is getting closer to the top of the list. If decided to add a second vent line on the opposite side of the boat I should have two fittings into the tank and not just tee off a single fitting?

 

[HeadedToTexas]

The "protruding" pipe need not extend more than 1/2" inch below the Uniseal.

Very good points. So understanding the impact connections on the side of the tank have on usable volume, a vent tube that protrudes ½ inch below the top of the tank has no impact because that volume was not usable anyway. My connections are well below the top.

It makes me wonder about the reported 30 gallon capacity. I see specs on newer Mariner 37s and Helmsman 38s indicating larger holding tanks. Is that a mathematical difference based on hose connections, or a physical difference based on a larger tank. Any of you owners of newer models (Escape is hull 3) have pictures of your holding tank you could share?

 

[HeadMistress]

Thanks for the info Peggy, this winter I plan on seeing if I can finagle my tank out and redo my vent line to a larger mushroom type. and I will check the discharge pipe also. Plan to replace all the waste lines also. Slowly working down my list but the waste smell is getting closer to the top of the list. If decided to add a second vent line on the opposite side of the boat I should have two fittings into the tank and not just tee off a single fitting?

I would go with aeration instead of a second vent line (which would need a second thru-hull) 'cuz unless your vent line(s) are relatively short, straight and don't rise more sharply than 45 degrees, a second one wouldn't help much.

Aeration doesn't have to be expensive...many owners DIY aerators using a bait box pump and some "perforated" (put holes in it) hose. that can deliver air throughout the tank. It does have to run 24-7 whether you're on the boat or not (see my previous posts on this), but the current draw is minimal.

--Peggie

 

[CharlieO.]

I would go with aeration instead of a second vent line (which would need a second thru-hull) 'cuz unless your vent line(s) are relatively short, straight and don't rise more sharply than 45 degrees, a second one wouldn't help much.

Aeration doesn't have to be expensive...many owners DIY aerators using a bait box pump and some "perforated" (put holes in it) hose. that can deliver air throughout the tank. It does have to run 24-7 whether you're on the boat or not (see my previous posts on this), but the current draw is minimal.

--Peggie

What is your definition of relatively short? I could one side at probably a bit less than 5’ and the opposite side with maybe 7ish’ with a slight uphill definitely might much less than 45 degree.

 

[Comodave]

My boats beam is about 14’. I put a 1.5” one to each side. They go up less than a foot each so it is pretty much a straight shot from side to side.

 

[CharlieO.]

My boats beam is about 14’. I put a 1.5” one to each side. They go up less than a foot each so it is pretty much a straight shot from side to side.

How high above the waterline are they?

 

[Comodave]

I have not measured it but it is about 1’ 6”.

 

[CharlieO.]

I have not measured it but it is about 1’ 6”.

Thanks, I will be a little more than that. Did you do two vent fittings on the tank?

 

[Comodave]

Yes, 1 from each side so the air will come in one vent and flow across the sewage and out the other vent. It isn’t as good as going in one side and out the other end since my tank is rather long but it was the best I could do. Even then I had to have the mechanic come and hook the hoses up since I couldn’t fit back there with my back problems, I couldn’t contort my back to fit in there. In the past I never had anyone do work on my boat but now I have to.