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Black tank Burp while draining.


engine103
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Okay, while draining black tank all will go well until it pulls a vacuum and the flow stops. If I go into the coach and flush the toilet it will dump out the black gate like crazy until empty. Next switching to the grey tank, same thing until I open the outside hand washing faucet then all flows well.  I have run a garden hose down the vent pipes to clear any possible obstructions and don't believe I have any (odd it would be in clogged in both tubes). Is there a vacuum valve I might be missing? I know there are some work-around solutions I can do but I would rather solve the problem. 

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There are usually vacuum breakers under the sinks. Also your black and gray tanks should be vented to the roof. There have been cases where the roof vent pipe slipped down into the tank and was obstructed. Of Course that can only happen if the vent pipe is a straight shot down.

 

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Thanks Bob, yes both tanks are vented through the roof and I have an easy view where they actually enter both tanks. Right now wind chill is 8 so I'll wait for a little warmer temp to re-inspect. Thought there might be a vacuum breaker in the wall behind the shower but would think both black and gray would have their own. Jim

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Hi Jim, since your piping should be the same or similar to ours and since you confirm that the vent pipes are clear as you have probably done by running water from a hose down the vents without them filling back up, I would suspect the external septic system. IFthe tank vents are in fact clear, I don't really understand how the external faucet would have any impact. Maybe be just a coincidence? Yes, the toilet would supply the displacement air while open but it would not be necessary with a clear vent pipe. I would turn my attention to the septic system. Good luck with this crappy situation!

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There's positively something wrong with the vent pipes between the tanks and the roof.  These are atmospheric vents that are designed to allow the tanks to breath.  While dumping, they're plenty big enough to allow all the air necessary into your tanks to drain properly.  I'd bet when you're able to try the roof top test of dumping water down those pipes, they're going to fill up and confirm your problem.  Hopefully for you they go straight down into the tanks making it easier to run something down through them to clear the blockage.  It might be those pesky muddubbers built their nests in the pipes and blocked them.  That would be an easy fix because they'd be right near the roof and they're water soluble.  Good luck in your quest!

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Thanks Moon! I'm sure your right even-tho I had (maybe not as good as I thought) ran a hose in the vent pipes last year and operation of the system seemed to be working okay. Mud Daubbers, Lord knows we have them and they can build nest in what seems like minutes. After looking at all the options, the vents have to be the problem. Fortunately it's a straight shot from the roof to the tanks. When the weather gets a bit warmer, I'll pull it outside and flush them again, thanks, Jim

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Jim,

Here is another thought. On occasion our gray tank will not drain and I can fix this by picking up on the sewer hose or opening the black valve with the gray valve open. I suspect that the person at the factory who cut holes in the gray tank let the large cutout piece fall into the tank and now and then it ends up over the output. Some day when I get around to it, do you have any spare roundtoits😀, I plan to put a camera into the tank and see what is there.

 

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