Can't pump out holding tank

[waterman46]

Have you determined that the holding tank is a hard shell design or is it possibly a collapsible bladder type? The bladder tanks have the fill (from head), vent and pumpout connections all on the top of the bladder, so the pumpout hose connection must be able to move freely downward as the tank is emptied. If air from either the vent or the head can get into the tank when you are trying to pump out and the pumpout connection can't move down to the level of waste in the tank, you may not be able to pump out all the waste since air from the vent or head will just be sucked into the tank and flow back out through the pumpout hose.

This only applies to flexible bladder tanks, just thought I'd mention it since you didn't confirm the type of tank you have.

[roland stockham]

You do mention that the tank has notbeen used much. Consolidation of solids causing a blockage could well be the issue. It might be cleared by water ormayneed a chemiical agent as well, check compatability with valve and sealsbefore use! Also going for a brisk sail is a good way to shake things up.

[Bigjim]

I removed the wire screen on the vent and yes it did have some gunk on it. But I also think I may have identified the issue with the head.

The pump-out hose has a y-valve on it because the boat was originally equipped to discharge overboard. The y-valve looked like it was wired in one position. But I just tried it today and discovered it was NOT wired in placed.

So, the pump-out was probably not connected to the holding tank when we tried to pump it out. We will try it again this week.

[peghall]

If that does turn out to be the problem, you still need to make sure the vent is open, so I hope you backflushed it after you got rid of the screen in it, 'cuz if there was a gunk in the screen there's also likely to be at least a partial blockage at the other end too.


And unless you plan to take the boat into waters where it's legal to dump the tank and/or flush directly overboard, I'd get rid of the y-valve and any overboard plumbing from it too.



--Peggie

[Bigjim]

SUCCESS! I found the holding tank under the v-berth in the forward cabin. It is a hard tank with an in-hose and an out-hose with a separate vent. The tank was nearly half full.

We took the boat over to the pump-out and tried again. At first it didn't work, so I put my wife on pump-out duty while I climbed down into the cabin and reached under the cabinet and started playing with the y-valve. Turning it one way got no result, turning it back at first did nothing. But I worked the valve back and forth while she held the hose to the pump-out port. FINALLY, the contents started to flow out of the tank!

When it finished I could hear some air being sucked in from the bottom pump-out connection. So, there's a small leak in the fitting. I'll have to remove the hose and seal the leak.

Wow, that's a load off my mind (and my boat).

[Bigjim]

A further note about the pump-out. I think that the problem is the power of the pump-out. I think it is too strong. When I turn the Y-valve completely toward the holding tank nothing happens. I think the vent hose is collapsing.

Then I turn the Y-valve to the overboard discharge and nothing happens.

But, then, I turned the Y-valve half-way between the two positions and then you can hear it sucking the contents. It even sucks the water out of the toilet itself.

[peghall]

When I turn the Y-valve completely toward the holding tank nothing happens. I think the vent hose is collapsing...But, then, I turned the Y-valve half-way between the two positions and then you can hear it sucking the contents. It even sucks the water out of the toilet itself. ..

The vent is definitely blocked. The pumpout is sucking the water out of the toilet because the toilet is the only available source of air it needs to prevent pulling a vacuum. And be glad it can, because if the pumpout is stronger than average, without any air coming in to replace the contents it's trying to pull out, it could implode your tank.


--Peggie

[GrowleyMonster]

If your vent hose is clear vinyl, replace it with the white reinforced hose.

[Bigjim]

Originally Posted by waterman46

Have you determined that the holding tank is a hard shell design or is it possibly a collapsible bladder type? The bladder tanks have the fill (from head), vent and pumpout connections all on the top of the bladder, so the pumpout hose connection must be able to move freely downward as the tank is emptied. If air from either the vent or the head can get into the tank when you are trying to pump out and the pumpout connection can't move down to the level of waste in the tank, you may not be able to pump out all the waste since air from the vent or head will just be sucked into the tank and flow back out through the pumpout hose.

This only applies to flexible bladder tanks, just thought I'd mention it since you didn't confirm the type of tank you have.

There is a huge difference between a hard tank and soft-sided holding bladder. I guarantee you I know the difference.

The problem is the y-valve. I think they put it in incorrectly. On my next opportunity, I’m going to remove the valve and put a Single hose in in its place. No vent air gets in during pumping out.

Originally, I thought it was because of the soft vent hose, but when we pumped out last, there was still no vent air getting in. So, I had to play with the y-valve as before and heard air being sucked through the toilet.

I think the valve was installed in a way to connect the deck pump-out to the overboard through-hull and from the holding tank to the overboard discharge, so neither position goes from the tank to the deck pump-out. When the y-valve is in the halfway position the tank pumps out. That tells me the valve is the problem. BTW, when the valve is in that position I can also hear air being sucked through the new vent hose.

[Bigjim]

Originally Posted by peghall

When I turn the Y-valve completely toward the holding tank nothing happens. I think the vent hose is collapsing...But, then, I turned the Y-valve half-way between the two positions and then you can hear it sucking the contents. It even sucks the water out of the toilet itself. ..

The vent is definitely blocked. The pumpout is sucking the water out of the toilet because the toilet is the only available source of air it needs to prevent pulling a vacuum. And be glad it can, because if the pumpout is stronger than average, without any air coming in to replace the contents it's trying to pull out, it could implode your tank.


--Peggie

Peg, Thanks for all your wonderful advice and counsel. But in this instance I think I’ve found the problem. The vent is not blocked. I believe the problem is the y-valve. I think they installed it wrong. I believe they set to go from deck to thru-hull (A) and from holding tank to thru-hull (B). Neither position goes from the deck pump-out to the holding tank. When I turn the valve halfway, the tank pumps out and I hear air going through the vent hose too. I’m going to remove the y-valve altogether because it’s against the law to discharge waste overboard in the Great Lakes. So no need for that option until I start my world cruising.

[peghall]

Well, I'll be darned...there went my perfect batting average! Or maybe not.

Good catch with y-valve...not many people would think to try it half open. That the pumpout may be able to pull in some air via the vent means it's not totally blocked, but if the pumpout continues to pull water out of the toilet after you've removed the y-valve, there is a partial blockage in the vent, most likely in the vent thru-hull but can also be at the other end of the vent line--that end of the hose and in the vent fitting on the tank. So you'll want to scrape out both locations just to be sure. And as long as you're doing a little surgery on the system, now would be a good to replace the "vent" thru-hull--which is designed to keep sea water out of water and fuel tanks--with an open bulkhead or "mushroom" thru-hull that you can put a hose nozzle against to backflush the vent line every time you wash the boat and/or pump out...preventing future vent blockages.

--Peggie

[Bigjim]

Originally Posted by peghall

Well, I'll be darned...there went my perfect batting average! Or maybe not.

Good catch with y-valve...not many people would think to try it half open. That the pumpout may be able to pull in some air via the vent means it's not totally blocked, but if the pumpout continues to pull water out of the toilet after you've removed the y-valve, there is a partial blockage in the vent, most likely in the vent thru-hull but can also be at the other end of the vent line--that end of the hose and in the vent fitting on the tank. So you'll want to scrape out both locations just to be sure. And as long as you're doing a little surgery on the system, now would be a good to replace the "vent" thru-hull--which is designed to keep sea water out of water and fuel tanks--with an open bulkhead or "mushroom" thru-hull that you can put a hose nozzle against to backflush the vent line every time you wash the boat and/or pump out...preventing future vent blockages.

--Peggie

I found the issue by accident. The pump out could not suck anything from the tank at all. I knew there was a y-valve and thought the last owner left it in the overboard discharge setting, but when I flipped it over to the other side, still nothing happened, but I heard air going through the line when it was "halfway" open. I started jiggling it back and forth and was able to pump out the tank.

At first, I thought the same as you and figured the vent was clogged (from one of your previous comments). I punched out the wire mess in my vent thru-hull, thinking it was clogged or blocked. Still no joy. Then, I figured it was the soft vent hose collapsing due to the excessive suction. But when I replaced the flimsy vent hose with a reinforced hose there was no improvement and I still had to jiggle the y-valve.

I will confirm the diagnosis when I finally remove the y-valve and conduct the next pump-out. Either way, I don't need the overboard discharge while I'm still in Lake Michigan. So, I'm hoping this puts an end to this problem.

[GiniL]

Hi all. I'm a new member of the forum, but for several years have been a lurker. This is my first time to need to seek advice that hasn't already been given.

I'm tagging onto this post because it is the most relevant thread I have been able to find. I am not able to pump out my holding tank using a dockside marine vacuum pump. I'll offer first a few background into items, then a list of what I've discovered so far. I'm hoping someone can tell me where to look next.

Background:

• The boat: two years old. New when purchased.
• Holding tank usage: Light use, mostly liquids, some solids, only occasional
• Past pump outs: I've done three on not very full tanks. A fourth was with a tank about half full (June 2020). On that one, I wasn't sure I got everything out before cavitation started. I added water and pumped out again. It seemed like I got the added water out. Now I'm less sure that everything came out on that "big" pump out, either before or after adding the fresh water.
• Current issue: After 17 days aboard in December 2020, with two to three women aboard and liquids only (no solids and little or no tp once a guest was reminded), the tank was 1/2 to 2/3 full. When I went to pump out, nothing, nada. I thought it was a bad pump, but then went to two others and had the same experience. This was the first time nothing would pump out.

What I discovered so far:

• I started with the vent (yes, I have Peggie Hall's book, both the old edition and the newer one, and I follow all her advice, so I knew to look there first.)
• Sure enough: The opening of the vent was plugged! But not with waste. It was plugged with polyurethane caulk from the original installation. There was a small hole in it, so that it was about 80% to 90% plugged, rather than fully plugged. But the plug was substantial. (How the heck did I ever pump out at all???) I thought I had found the culprit for sure.
• After removing the vent fitting, I shot water down the vent line. It seemed to go down fine. It also went down the discharge line to the pump out fitting just fine (no change there; water had gone down fine before).
• I went to a pump out station and tried again, leaving the vent fitting off the vent line entirely. So the line was wide open (taped in place). But, NO! The pump still couldn't pull from the discharge fitting.
• At that point, back at my dock, I checked the macerator pump discharge, using a bucket to catch what came out of the above-water-through hull. It came out with full force. We started and stopped quickly. But it worked fine.
• Then I went after the other end of the vent line. Hard to get to, but I squeezed in and finally got the line off the barbed fitting (cursing all the way). The line and the port into the tank both were totally clear.
• With a friend's help and his transfer pump, we used the vent opening into the tank to get most of the contents out and into a portable transfer tank.
• I reattached the vent hose and put in about 10 gallons of fresh water, and some Raritan KO. I let it sit for a couple of days for some good sloshing action.
• I then went back to the pump out just to see if anything had changed. It hadn't. No go. That's where I am at this point.
• FWIW: There is no inspection port on the tank. The discharge hose to the macerator and the one to the pump out fitting both draw from the top of the tank. The tank is thick, heavy, highly opaque polyethylene. As best I can tell, the dip tubes are intact. The discharge hoses themselves are difficult for me to reach, and the space is so tight that I wouldn't be able to get them off if I could. If it comes to that, I'm enlisting help (younger, stronger, and probably a professional).

But I'm stumped on where the problem is at this point. All hoses still look brand new (no splits, etc). The tank looks fine. On my last attempted pump out, I put water in both toilet bowls and it was there after my effort.

So I'm at wits end and would welcome thoughts, suggestions, condolences. Anyone? And of course, Peggy Hall, if you aren't enjoying your retirement free from trying to solve the world's marine head problems!

Thanks in advance.

Gini

[GrowleyMonster]

Possibly the suction pipe or hose has come loose from the fitting that your discharge hose connects to on the top of your tank. Or it could be clogged. Open up your deck fitting and go in with a plumber's snake. When you think it has hit the bottom of the tank, have somebody continue to poke it down while you listen at the tank, and try determine if the end is striking the tank bottom or not.

PRO TIP: you would think that you could just connect regulated compressed air to the vent fitting and gently push the contents up through the deck fitting and out a temporary hose into a portable tank, right? I know someone who did that, and it ended badly. Those tanks are not pressure rated!!! Nor are any glued in place fittings. So don't use compressed air for troubleshooting unless you are willing to risk having sewage blown all over your boat. Ewwww. If you want to risk it, just know that it takes 3psi to raise water a bit over 6 feet. 5 psi will raise it about 11.5 ft. If you are showing 5psi on the air, and nothing is coming out the top, not even air, then you have a solid clog. If there is a lot of sewage in the tank but only air comes out, then your suction hose going to the bottom of the tank is leaking or no longer attached at all.

One of these little gadgets can be really handy.
https://www.amazon.com/Seesi-Endosco...1553839&sr=8-9

My best guess is that your internal suction hose or pipe from the tank top to the bottom of the tank is leaking, and when you put a suction on the system with the pumpout sucky hose, you are just pulling air through the vent hose, across the interior of the tank, through the leak and uot the deck fitting into the pumpout. hose and pump. There are a few kludgy repairs you could try but I won't bore you with them. With no inspection port you will have to cut one, probably, or drop a smaller diameter hose down the suction fitting of the tank and seal it in place, then connect to the deck fitting throuch a reducer. This might work since you have a powr macerator. It is possible that you will end up having to replace the tank, depending on how it is set up internally. Adding an inspection port isn't really a big deal, though. But a small tank isn't going to break the bank.

<EDIT> Are you sure that your head is discharging into your tank? If you have a 3 way valve, make sure it is lined up properly or you are flushing overboard! Ditto if you have the same thing but just made from discrete valves. Also try filling your tank through the deck fitting by pouring a few gallons of water down it. Don't use a hose for that. You won't know how much water you have put in.

[Mike Banks]

I think this sort of question has come up before--but the first question I would ask is if your heads is an electric macerator type or a pump-and-pray?

Macerator types seldom give trouble, but the fault may not even be yours. Do you know just how good the suction pump on the collection vehicle really is? If the tide is out and your vessel is below the truck or the discharge suction line, lotsa luck..

If you have a sullage pump aboard. I had one on mine--it was a diaphragm type driven by a little cross-head plunger. It emptied the holding tank in a few minutes. Five minutes or so to empty if the tank was not too full.

Incidentally, the pump out to deck fitting is a pipe going to the bottom of the tank with an inch or so bottom clearance. The tank NEVER empties fully from that outlet because it has to terminate clear of the bottom of the tank. It is only if I use the pump-out drain valve and the sludge pump that I can get the tank almost dry. This outlet has choices of overboard via a siphon breaker, or I can fit a hose to the pump outlet and pump it on to a wharf if necessary. Pumps will always push more waste than they will suck, and you need a discharge hose of at least two inches internal diameter. The longer the hose, the more difficult a job it is for the pump.