Pump Out Macerator Pump filling holding tank

Hi there, 2004 Mainship Pilot 30, seems I'm gaining water vs relieving water! I empty my tank underway, and look a bit later, and tank is full again. I'll assume there is some kinda check valve in the macerator pump? I'm guessing its an origional pump, shoulda taken a picture, but forgot. Is the fix to replace the pump, or is there soemthing easier? Kinda tight in there! Guess I'll have to do it the old fashion way, shut off the seacock to the macerator and pump out at the pump out station thru the deck fitting in the mean time. BTW,. it's a salt water head.

OK, I am curious to know why.
Is this a new event, as in was it working correctly and now does not. Is the thru hull below water line and is the macerator also below water line.

Yes and Yes, This is a new event, my tank was not filling up on it's own before, and the thru hull is below the waterline, the Macerator pump may be about even with the waterline, give or take an inch, mounted just above the seacock behind the holding tank. I figure I can close the thru hull when I get to the boat tommorrow AM, and go to a pump out dock and pump the tank dry, however, will need to fix eventually, unless there is a quick fix, someone is aware of? I'm guessing a 20 year old pump has lived it's life well in a salt water environment.

Before blaming the pump - check the anti-syphon valve you have in the pump out hose - if blocked it could be sucking the discharge right back in - with a lot of sea water of course

Hummm, I don’t recall seeing an anti siphon valve in the train from the end of the holding tank to the sea cock anywhere. I’ll try to post a picture tomorrow when I get there, and let you guys tell me what you see. Thanks!

There should be a vented loop in the tank discharge line between the macerator pump and the thru-hull...bu in the absence of one there's another simple solution:: keep that thru-hull closed except when dumping the tank and be moving very slowly when you empty the tank. Macerator pumps can slow down water being forced up them through an open thru-hull, but they can't block it completely..

--Peggie

Thanks Peggy, That’s obviously a solution, but I guess I still have to ask, the tank never filled itself before, now suddenly it’s doing it. Am I correct in my assumption that the pump is just on its last legs, or is there something else there? Thank you!

AS suggested close the thru hull valve, go to you dump site and empty tank, then immediately close valve. Confirm tank is empty.
Remove the pump from hose between thru hull and pump. If there is no backflow preventer then the vanes in pump are allowing water in.
Oh, and as Peggy said there should be a vented loop since this is below waterline. I am guessing you do not have a vented loop.

Ok, So the backflow preventer is connected between the end of the Mac pump and the hose to the seacock, I’ll look for it. Please understand that these Pilot 30s have big boy systems in little boy spaces, so seeing things and especially working on things is a real challenge! As for the vent, the holding tank has a vent, but I’m guessing you are referring to something different. I’ll update tomorrow either after I pump out of after I get to the Island. Thank you!

Not exactly. You either have a backflow valve or a looped line. You need to determine which one was keeping water filling the tank.
My guess is you do not have a looped line and may have a backflow that is not sealing. So look for a loop line before taking things apart.

Ok, So the hose from the top of the seacock goes straight up to about the Mac Pump, does a U down, then a U back up to connect to the pump, call it a 5/8 ish inch hose, it doesn’t loop in a circle, but forms an upside down U if that makes sense?

Mainship Pilot said:

Ok, So the hose from the top of the seacock goes straight up to about the Mac Pump, does a U down, then a U back up to connect to the pump, call it a 5/8 ish inch hose, it doesn’t loop in a circle, but forms an upside down U if that makes sense?

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Perfect sense. should have said it like that to you. The top of the loop is well above water line, correct? Then the little breather at the top of the 'U' is called an anti siphon that lets air in to stop backflow. It is most likely plugged. That is where you start. Clean if possible, replace otherwise.
Even after fixing, close the seacock when not in use.

Will do, will check it out tomorrow when I get there, don’t remember seeing a breather, just the hose, but that doesn’t mean it’s not there. Thank you so much!

Here’s pix. shut off seacock and emptied head.

Where does the blue stripe hose connect, under to the macerator?
Where does the white hose connect, to the bottom or top of the holding tank?

From what is pictured you do not have a backflow or a vented loop above waterline from the thru hull.

Yes, Bottom of Pump and bottom of tank. I’ll be shutting the seacock off from nowon!

Mainship Pilot said:

Hi there, 2004 Mainship Pilot 30, seems I'm gaining water vs relieving water! I empty my tank underway, and look a bit later, and tank is full again. I'll assume there is some kinda check valve in the macerator pump? I'm guessing its an origional pump, shoulda taken a picture, but forgot. Is the fix to replace the pump, or is there soemthing easier? Kinda tight in there! Guess I'll have to do it the old fashion way, shut off the seacock to the macerator and pump out at the pump out station thru the deck fitting in the mean time. BTW,. it's a salt water head.

Click to expand...

Didn't read all the responses, but did you close the seacock right away after dumping? If not, the holding tank will sometimes (often? usually?) back-fill...

-Chris

Had the same set up with a high point in the hose, but no vent or check valve. Mine also one day started backfilling the holding tank. It turned out to be vacuum created in the tank after pumping out, it would reverse the flow after the pump was off and suck water back in. Once started it just kept going until full.
Replaced my holding tank vent filter and flushed/cleaned the vent line for the tank. Don't forget the vent on the outside, if it has the small holes, they can get plugged with wax, or bugs. This solved my problem with better venting and no vacuum created in the tank.

Bill, I guess I missed this because it was not posted at the MS forum section which I monitor.

Firstly, shouldn't the through-hull always be closed unless you are pumping in waters where it is legal. The USCG will look at it if they board you.

Secondly, my same model boat is outfitted as yours, no check valve between pump and through-hull. Pump input is maybe an inch or so below the level of the waste tank outlet on the bottom of the tank and connected by a short length of 1.5" waste hose. I believe the tank bottom and mac pump to be below waterline, especially when cruising with the nose up. I am on the third mac pump now and given the vane pump nature of them revealed by autopsies, I am amazed you never had the waste tank backfill form the open through-hull before this.

For others' info, the 30 Pilot II layout back there under the cockpit deck allows for NO vented loop tricks because the deck itself is so close to the waterline, especially underway.

Rich, I have had the thru hull open since I bought it, so this is a new development. I've since closed it, opening only for dumping enroute to the island or returning mid channel. I guess with my prior 43' trawler, that the vacuflush system was all above the waterline, including the macerators, we got lazy and never closed them. I was boarded, but never addressed this, as dumping while crossing the Catalina Channel is commonplace here.

My boat has a similar issue. Top of the tank and the macerator are just below the waterline and water can slowly push back through the macerator into the tank as there's no vented loop in the discharge line. The simple solution is just to keep the seacock closed whenever the macerator isn't being used. Also avoids forgetting when entering waters where waste can't be dumped.

I think you guys might want to consult the regs on these waste line through hulls because it is my interpretation and that of at least one USCG boarding that they are required to be closed inside of the 3-mile limit and in any NDZ like Catalina. In your case, Bill, I could see where the pump's internal conditions have changed to allow this seepage, and if it allows inflow, I can imagine that it would also allow outflow once the tank level is very full. What if somebody pumped it while moored in Catalina where they stick that pill in your head upon arrival and it began to seep through that pump to the sea? OOPs. poops.

rgano said:

I think you guys might want to consult the regs on these waste line through hulls because it is my interpretation and that of at least one USCG boarding that they are required to be closed inside of the 3-mile limit and in any NDZ like Catalina. In your case, Bill, I could see where the pump's internal conditions have changed to allow this seepage, and if it allows inflow, I can imagine that it would also allow outflow once the tank level is very full. What if somebody pumped it while moored in Catalina where they stick that pill in your head upon arrival and it began to seep through that pump to the sea? OOPs. poops.

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That's exactly why I don't consider backflow a problem. The valve should be closed 99% of the time anyway and only opened when needed. On my boat the normal position is macerator seacock closed and ziptied, macerator breaker off. Plenty to keep the USCG happy, as you'd have to go down, cut the ziptie, open the valve, walk over to the panel, turn the breaker on, then walk to the galley and hit the dump switch before any waste would be discharged.

Toilet install and boat design 101:

If your discharge is below the waterline you need a vented loop. This loop is part of the 1 1/2" ( or so) discharge line from the pump and through a loop that does a U well above the waterline. At the top of the loop is a vent break that is called an anti-siphon valve. The loop continues to the below the waterline discharge point.

The purpose of this loop is simple - it keeps your boat from sinking. Plus it keeps salt water from entering your plumbing system. We had 6 loops on our DF 48, fail safe after nearly 20 years.

Don't forget the vent on the outside, if it has the small holes, they can get plugged with wax, or bugs. This solved my problem with better venting and no vacuum created in the tank.

Better yet, replace the "vent" thru-hull with an open bulkhead fitting (same thru-hull that bilge pumps use. "Vent" thru-hulls are designed to keep sea water out of water and fuel tanks...boatbuilders use them on holding tanks too because it costs them less to just use the same thing on all vent thru-hulls and they've never bothered to learn that sewage--unlike fuel and water--requires management, ignoring the need for air exchange via the vent. An open thru-hull provides that air exchange, plus it allows you to prevent vent blockages by putting a hose nozzle against it to backflush the vent line regularly, sending anything that's trying to set up housekeeping in in it into the tank, something that cannot be done using a "vent" thru-hull.

--Peggie