After flushing WC (the jabsco WC with a hand pump) into the holding tank, in a few minutes about a gallon of waste backs up into the toilet. It bubbles back up. At first I thought it was because the tank was very full, but after dumping the tank, it still does the same thing. The vent hose does not appear to be stopped up, but before I take it off, I wonder if others have had this problem and found the cause?? I have a macerator pump that has a vented loop leading to a through hull. It has always worked well since I installed the pump and new lines over 5 years ago.
holding tank backs up
- Thread starter sunwindsea
- Start date
If there is anything in the tank and it is pressurized, the contents will come out before the pressurized air.
I'd remove the vent line from the tank.
Lots of info on that in the plumbing and sanitation forum. Peggie Hall recommends this:
" But just in case there's any pressure in the system , you'll want to relieve it before removing the vent line from the tank to clean them out...so open the deck pumpout fitting VERY CAREFULLY with a hose at the ready. Be sure you're UPwind of it! Scrape out that end of the vent line and the vent fitting on the tank...replace the vent line. "
You can't change physics......if the tube to the pumpout is in the liquid it will either do nothing or if there is enough pressure in the tank to raise the liquid in tank to the opening, it will release liquid. If there is enough pressure but not enough liquid to fill the tube then you will have a poo volvano It would need roughly .434psi to raise it each foot, assuming the tube is at least a square inch. I have great respect for Peggy, I've have her book and currently using it.
I'd be interested on how much pressure the pump could generate.
I'm having the same problem. I know it's not air pressure from a plugged vent. Besides, I can open the deck cap and it still occurs. Pretty sure it just a failed joker valve. There never is enough liquid to overflow the toilet. I'm going to do the Raritan LBA Upgrade this winter.
You've just described all the symptoms of a blocked holding tank vent.
All tank vents have two main functions: to provide an escape for air displaced by incoming contents and provide a source of air to replace contents as they're pulled out. When air displaced by incoming waste cannot escape out the vent the tank becomes pressurized, creating increasing back pressure that prevents the toilet from flushing.
Without a source of air to replace contents as they're being sucked out of the tank, the pump will pull a vacuum that'll prevent it from pulling out more than a gallon or two. A particularly strong pumpout can even implode a tank.
When air displaced by incoming waste cannot escape out the vent the tank becomes pressurized, creating increasing back pressure that prevents the toilet from flushing.
Do NOT use the toilet again or try to pump out or dump the tank until you've cleared the vent. Without a source of air to replace contents as they're being sucked out of the tank, the pump will pull a vacuum that'll prevent it from pulling out more than a gallon or two. A particularly strong pumpout can even implode a tank.
The two most common locations for a vent blockage are the vent thru-hull and the other end of the vent line--that end of the hose and the vent fitting on the tank. Start by cleaning out the thru-hull...use a screwdriver blade, ice pick--whatever works. If that doesn't result in a spew out the vent, you'll need to relieve the pressure before removing the vent line from the tank to clean them out...so open the deck pumpout fitting VERY CAREFULLY with a hose at the ready. Be sure you're UPwind of it! Scrape out that end of the vent line and the vent fitting on the tank...replace the vent line.
If there's a filter in the vent line, remove it...once a filter gets wet--which can happen when a tank is overfilled or even due to heeling--the charcoal swells and blocks the vent...one of the reasons why vent filters aren't recommended for use on most sailboats.
--Peggie
Nope...it's not. And opening the deck pumpout cap can't help much if any unless the tank is empty or almost empty because the the other end of the pumpout line is at the bottom of the tank ...while vent lines are above the surface of the tank contents.
That can only happen if the tank vent is blocked, creating the pressure, Mike.
--Peggie
Peggy, I’m going off of the previous post that there is assumed pressure built up in the tank and removing the deck cap will relieve it.
We are saying the same thing regarding your and my above explanation.
By the way, using your book, I installed my mushroom type through hull last night and found the hooded fuel vent type through hull with a galvanized elbow on the inside that wasabout 3/4 plugged with corrosion. I’m also looking forward to the effects of the Raritan Ko and towel bowel cleaner.
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I misread your post...sorrry! While opening the pumpout cap will not provide air to replace a blocked vent (I see a lot of posts from people who think it will), that will relieve the pressure. Just be sure you're UPwind of the fitting and have a hose at the ready...something I learned the hard way.
If your tank still isn't getting enough air for KO to prevent odor out the vent entirely (it needs a lot), switch to No-Flex Digestor Noflex Digestor . Not sure what you mean by "towel" bowl cleaner though.
--Peggie
If your tank still isn't getting enough air for KO to prevent odor out the vent entirely (it needs a lot), switch to No-Flex Digestor Noflex Digestor . Not sure what you mean by "towel" bowl cleaner though.
--Peggie
Taking off the cap will de-pressurize the tank. It doesn't matter where that hose goes.
Maybe this will help...
Assuming the deck fitting pipe goes to the bottom of the tank and lets assume the pipe from the level of the liquid to the deck fitting is 1 ft and it is 1 square inch in diameter. In our discussion the tank has liquid. Let's assume it is just water. The tank is presurized from the toilet pump and due to the vent being 100% blocked.
In this example the tank would have to be pressurized, and remain pressurized to a little under 1/2 psi to have the liquid rise to the level of the deck fitting (1ft). The only way for the pressure to be equalized to atmosphere is to evacuate the liquid to a level below the intake of the hose allowing tank pressure (air) to equalize with atmospheric pressure.
So it does matter. This is why the vent line is installed on the top of the tank. If filled with liquid, the tank has to built pressure to force it out to allow passive air movement after.
Assuming the deck fitting pipe goes to the bottom of the tank and lets assume the pipe from the level of the liquid to the deck fitting is 1 ft and it is 1 square inch in diameter. In our discussion the tank has liquid. Let's assume it is just water. The tank is presurized from the toilet pump and due to the vent being 100% blocked.
In this example the tank would have to be pressurized, and remain pressurized to a little under 1/2 psi to have the liquid rise to the level of the deck fitting (1ft). The only way for the pressure to be equalized to atmosphere is to evacuate the liquid to a level below the intake of the hose allowing tank pressure (air) to equalize with atmospheric pressure.
So it does matter. This is why the vent line is installed on the top of the tank. If filled with liquid, the tank has to built pressure to force it out to allow passive air movement after.