Just recently removed my aluminum holding tank and replaced with polyethelene. Replaced all hoses with the exception of the vent line. The head flushes OK but as the bowl is cleared the very last portion seems to have some pressure behind it and is propelled above the rim. There is no pressure at all on the pumping mechanism. The only thing I altered when changing out the holding tank was to remove part of the vented loop on the vent line. This was necessary because the vent line would not reach the fitting on the new holding tank. Did I screw something up? I would have replaced the vent line but could not find a replacement locally.
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Vent line shouldn't have a vented loop
The purpose of a vented loop is to break a siphon...since nothing but air is supposed to pass through a vent line, there's no need for a vented loop in it. Two things puzzle me: 1. a vented loop is a single piece of bronze or PVC pipe bent into a 180 degree radius...how did you manage to remove only part of it? (A better question might be, what did you actually remove?) 2. If you could find sanitation hose locally, why couldn't you find hose to replace the vent line too? Just how have you plumbed your new tank??? 'Cuz whatever you've done seems to have created vent blockage that's pressurizing your tank.
The purpose of a vented loop is to break a siphon...since nothing but air is supposed to pass through a vent line, there's no need for a vented loop in it. Two things puzzle me: 1. a vented loop is a single piece of bronze or PVC pipe bent into a 180 degree radius...how did you manage to remove only part of it? (A better question might be, what did you actually remove?) 2. If you could find sanitation hose locally, why couldn't you find hose to replace the vent line too? Just how have you plumbed your new tank??? 'Cuz whatever you've done seems to have created vent blockage that's pressurizing your tank.
I probably mistated when I said vented loop. It was just a loop extending above the vent and then back down. I used part of this loop to extend the hose enough to reach the fitting on the tank. The tank is plumbed correctly. All hoses are connected to the proper fittings. Don't see how I could have created blockage here. In troubleshooting the problem I removed the pump out cap to make sure the tank was vented and still had the same problem.
Hmmmm....
Have you checked the vent through hull to make sure it's not clogged? Removing the pumpout cap will relieve any pressure in the tank, but because the pumpout hose fitting is at the bottom of the tank below the surface of the contents, it doesn't provide the same free flow of air that a vent above the surface does. Tank contents will be pushed up the hose ahead of the air...which is why a pressurized tank erupts instead of only "burping" air. So you could still get some backpressure in the toilet till there's enough pressure in the tank to push tank contents and air up the pumpout hose. So check your vent thru-hull. And while you're at it, straighten out the vent line...it doesn't need a loop, in fact should be as straight as an arrow. If you're concerned about taking on water through it when heeled, put a clamshell over it. If there are any tight bends in your head discharge line, check it again to make sure the problem shown in the attached photo hasn't happened. If the problem isn't in the new plumbing, it has to be in the toilet...make/model/age? Last time it was rebuilt (if ever)? Joker valve replaced?
Have you checked the vent through hull to make sure it's not clogged? Removing the pumpout cap will relieve any pressure in the tank, but because the pumpout hose fitting is at the bottom of the tank below the surface of the contents, it doesn't provide the same free flow of air that a vent above the surface does. Tank contents will be pushed up the hose ahead of the air...which is why a pressurized tank erupts instead of only "burping" air. So you could still get some backpressure in the toilet till there's enough pressure in the tank to push tank contents and air up the pumpout hose. So check your vent thru-hull. And while you're at it, straighten out the vent line...it doesn't need a loop, in fact should be as straight as an arrow. If you're concerned about taking on water through it when heeled, put a clamshell over it. If there are any tight bends in your head discharge line, check it again to make sure the problem shown in the attached photo hasn't happened. If the problem isn't in the new plumbing, it has to be in the toilet...make/model/age? Last time it was rebuilt (if ever)? Joker valve replaced?
Thanks for the response. The toilet is a Jabsco. I know not your favorite, mine either. Completely rebuilt within the last 6 months. I will take your advice on straightning the vent line. Will let you know. Any other thoughts please advise.As for tight bends in the discharge hose, yes there is. Where the discharge line leaves the head it makes a 90 degree turn to run aft. Poor design on Hunters part. No other way to run the line.Thanks
That tight bend can be solved by replacing
the straight discharge fitting on the toilet with a 90. It can be rotated to aim in any direction. You can get one from Jabsco. Without actually being there to trouble-shoot the system myself, I don't know what else to suggest to you...my psychic powers from here can only do so much. All I can tell you is, something is creating backpressure...find it, and you'll solve your problem.
the straight discharge fitting on the toilet with a 90. It can be rotated to aim in any direction. You can get one from Jabsco. Without actually being there to trouble-shoot the system myself, I don't know what else to suggest to you...my psychic powers from here can only do so much. All I can tell you is, something is creating backpressure...find it, and you'll solve your problem.
Pump Out
I feel your pain, and the vented loop "breaks" the siphon from your hose, back to the head. Without it, the FULL HOLDING TANK can seek it's own level, by returning to the bowl. I have had a similar problem, and am now attempting to solve it using a one-way valve, but it does not always work. On the good side, it lets me know when to pump out! I installed an electric Jabsco Base Conversion kit, and have had all types of problems, including what you are talking about. I don't want the vented loop either. Trying to eliminate smells. Note: Do not buy the Jabsco mentioned above. I can tell you why in another email, if you are interested. Mac
I feel your pain, and the vented loop "breaks" the siphon from your hose, back to the head. Without it, the FULL HOLDING TANK can seek it's own level, by returning to the bowl. I have had a similar problem, and am now attempting to solve it using a one-way valve, but it does not always work. On the good side, it lets me know when to pump out! I installed an electric Jabsco Base Conversion kit, and have had all types of problems, including what you are talking about. I don't want the vented loop either. Trying to eliminate smells. Note: Do not buy the Jabsco mentioned above. I can tell you why in another email, if you are interested. Mac
Oh dear, Mac...
"the vented loop "breaks" the siphon from your hose, back to the head. Without it, the FULL HOLDING TANK can seek it's own level, by returning to the bowl." The tank vent line has nothing to do with that, Mac. However a vented loop in the head discharge line won't necessarily stop an overfull tank from running back toward the toilet either...'cuz that's not a siphon, it's liquid being pushed through a line. "I have had a similar problem, and am now attempting to solve it using a one-way valve, but it does not always work." It's also a bad idea. If you'd like to tell me about the various problems you've had, I'll be glad to help you solve 'em without creating other worse problems.
"the vented loop "breaks" the siphon from your hose, back to the head. Without it, the FULL HOLDING TANK can seek it's own level, by returning to the bowl." The tank vent line has nothing to do with that, Mac. However a vented loop in the head discharge line won't necessarily stop an overfull tank from running back toward the toilet either...'cuz that's not a siphon, it's liquid being pushed through a line. "I have had a similar problem, and am now attempting to solve it using a one-way valve, but it does not always work." It's also a bad idea. If you'd like to tell me about the various problems you've had, I'll be glad to help you solve 'em without creating other worse problems.
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