Holding tank vent stack

[Outback 325BH]

Has anyone worked on their holding tank vent stack? I think I have one that sits too low in one of my gray tanks.

I'm going to measure how much water will go in the tank, via the galley sink, before pressure builds and halts the draining of the sink.

Are the stacks easy to get to once the coroplast is peeled back?


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[chuckster57]

Vents are attached at the TOP of the tanks so dropping the underbelly won't do much good.
Once you figure out which pipe it is on the roof, you can start removing wall panels.

[Outback 325BH]

Sure, they are on the top of the tanks, but wouldn't there be room between the top of the tank the floor? The pipe has to be fastened to the tank somehow, correct?


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[hankpage]

Your galley tank may not have a vent to the roof. It most likely has a mechanical (cheater) vent under the sink.. If this is not working correctly it may be causing your problem. Replacements are under $10. in home stores. JM2¢, Hank CHEATER VENT

[Outback 325BH]

The vents under the sink is to let air IN and prevents siphoning of the p-trap.

The tank stack is to let air OUT as the tank fills up.

Yes, I have a stack. It just sits too low in the tank, which prevents the sink from draining after the tank reaches 50% full.

Thanks.


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[chuckster57]

Originally Posted by Outback 325BH

Sure, they are on the top of the tanks, but wouldn't there be room between the top of the tank the floor? The pipe has to be fastened to the tank somehow, correct?


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Generally holding tanks are shoved up fairly flush to the bottom side of the floor. The drain and vent pipe are connected in one of two ways. Glued onto a termination fitting that is spin welded to the tank, or in a rubber grommet that is placed in a hole drilled on the top of the tank. Either way, if you remove the tank straps, you will need to access the top of the tank from the top side of the floor to re attach the drain and vent pipe.

With that said, I think your best course of action would be to locate the vent pipe and remove whatever walls you need to lay eyes on what type of fitting is on the tank. If it is a slip fit then you could easily remove the vent cap and pull the vent out, cut to the right length and reinstall.

After a nice dinner and some relaxing: your issue may be the drain pipe and not the vent pipe. We just had a class C that has this issue with the black tank. Tape measured the tank. 45" deep and then using the same reference point, were able to determine that the drain pipe extended 35" into the tank. Since it was the black tank we were able to remove the toilet and then the floor flange for repair. If the issue is the same thing on your gray tank, you still need to access the top of tank from the top of the floor.

[Outback 325BH]

Chuckster57, thanks for the insight. I found the wall I need to access. Hopefully my vent is not glued to the tank!


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