Manual holding tank pump-out clogged

[Ryban]

I believe there's a clog between my manual pump out and the holding tank. I say this because I can flush the toilet no problem, but I can't pump waste out through the seacock. I can perform one pump with the handle, but after that, it the handle won't budge much, and I can hear the sound of hissing air when I try to force it. My guess is a vacuum is forming, making it all but impossible for me to pump.

The only thing that has been put down the toilet is digested food, and small amounts of toilet paper.

Am I wrong to be hopeful that time will resolve this problem on its own? I did pour some vinegar into the toilet and flushed it, hoping it would help break down the clog.

[rbk]

There should be a shutoff and technically a lock out to make you legal in US waters. I'd go looking for a hidden valve.

[Ryban]

The seacock can of course be closed, and there's a vent for the holding tank, but the deck-level pump out was removed a long time ago.

It's a pretty simple setup and I don't see any hidden valves.

[rbk]

From the sound of it I wouldn't get inspected by the USCG. If it's creating a vacuum and there's no inline valve then it should draw from the tank vent. Something serious stopping the flow from head to manual pump. You could shut all seascoks remove a hose and snake it back to the head?

[Bleemus]

No pumpout? Dont get caught by the Coast Guard.

[peghall]

My guess is a vacuum is forming, making it all but impossible for me to pump.

That's a good guess...and I'd bet real money that a blocked tank vent is what's causing it. Tank vents provide an escape for air in the tank as it's displaced by incoming contents...if air can't escape the tank becomes pressurized. The vent also provides a source of air to replace contents as they're being pulled out. A pump pulling against a blocked tank vent will pull a vacuum that won't allow any more to be pumped out....which is just what yours is doing. That hissing sound is the pump trying to pull in some air from anywhere it can.

The most common locations for vent blockages are the vent thru-hull and the other end of the vent line, both that end of the hose and the vent fitting on the tank. Start at the thru-hull with a screwdriver blade, ice pick or whatever works to scrape it out. If that doesn't open it up, remove the vent line from the tank and scrape out that end of the hose and tank fitting. Ordinarily I'd tell you to open the deck pumpout fitting cap to relieve any pressure in the tank before disconnecting any hoses, but apparently you don't have a deck fitting, so instead I wouldn't use the toilet for a day or two to allow any pressure in the tank to dissipate.

[Kenomac]

What boat do you have? My friend's Hunter 450 had a similar problem, same symptoms when the level of sludge at the bottom of the waste tank built up to a higher level than the waste pumpout tube near the bottom of the tank. The bottom of the waste tube should be cut off at an angle so this doesn't happen and his was cut off straight across by a repair tech.

After you get this sorted out and are able to pump out again, it would be a good idea to give your waste system "enemas till clear" to dislodge all the sludge stuck to the bottom of your tank.

If your vent is plugged, it doesn't seem to me that you'd be able to flush your toilet. Your issue seems more likely to be an impaction.

[peghall]

My friend's Hunter 450 had a similar problem, same symptoms when the level of sludge at the bottom of the waste tank built up to a higher level than the waste pumpout tube near the bottom of the tank. The bottom of the waste tube should be cut off at an angle so this doesn't happen and his was cut off straight across by a repair tech.

About 25 degrees is the right amount of angle...any sharper leaves too much in the tank, any flatter is too easy to clog. This story also illustrates the reason why tanks should be thoroughly flushed out at least 2-3 x/season.


If your vent is plugged, it doesn't seem to me that you'd be able to flush your toilet.

If the toilet is only used by 1-2 people and it can be several hours or even overnight between uses, enough air can dissipate through the toilet to relieve the pressure created by the previous use to allow a few more flushes, masking the blocked vent. However, your point that a pickup tube cut flat across, too close to the bottom of the tank, could be his problem is well taken.

[Ryban]

I'm going to go for a swim in the morning and first see if it's the through hull/skin fitting by passing a wire up and down. Fingers crossed that this is the issue, but I have my doubts.

Otherwise I'll have to clear the blockage upstream... manually, it sounds.

[peghall]

What do you have to lose by cleaning out the vent thru-hull first?

[HopCar]

I second Peggy, it sounds like a blocked vent. That's the easiest thing to check. Why not take a minute or two to pass a wire through the vent before you move on to harder and far more disgusting things.

Hope it's not a blockage else where. That gets really messy.

[DeepFrz]

Saw a video where 2 girls went into the water to clear a blockage. They ended up swimming in poo. Not pretty but necessary I guess.

[Lucky]

I have had the same problem with a blocked outlet. This is how I solved it:
1 use a dingy pump and​pump air backwards from the outlet. You should be able to empty the tank.
2 when you succeed in getting flow out of the tank, close the overboard valve and pump in one litre of sulphuric acid (30percent strength)
Leave for 3/4hour, open outlet valve and flush out.
This worked perfectly fine for me and have not had a problem since.
Be aware that any metal in the system could be damaged by the acid. If it's​ all non metallic you will not have that issue.

Good luck!
Happy lead free sailing from Lucky

[jmac9365]

Have you checked the Joker valve I've seen them get inverted and you can't pump anything through it

[Ryban]

I disconnected the vent line to the holding tank, and cleared this portion, left the vent hose disconnected, and tried to pump, but still no luck.

I checked the outlet by running a zip tie up and down the through-hull, but this appears to be clear.

Can you clarify the dinghy-pump solution? It sounds like this might be a decent idea, but do I need to be worried about the manual membrane pump that is between the through-hull and the holding tank when pumping air backward through the line?

What is a joker valve?