Interesting observation

[JoeofNSB]

I have been plagued by a sewer smell when I dump my tanks. I have used every commercial tank deodorizers/cleaner and all of the homemade ones too. By the way, the homemade ones work the best!! I have always dumped the black tank first followed by the two grey tanks to flush the hose. I have always waited until they were very full before dumping and still a rotten smell inside the RV when I'm done.

Well, I'm glad to say that I have found the issue and my findings may help you. Apparently when I dump my tanks the exiting waste produces such a suction that the P-traps under the sinks and tub have the water sucked out of them and the smell rises through the now completely empty pipes.

Solved the problem by putting the drain plug in each sink and tub and filling up each with enough water to cover the plug. I then drain the tanks just as before and presto! NO SMELL.

Just a little nugget of info for a Sunday! y'all have a great day!

[SteveC7010]

Originally Posted by JoeofNSB

I have been plagued by a sewer smell when I dump my tanks. I have used every commercial tank deodorizers/cleaner and all of the homemade ones too. By the way, the homemade ones work the best!! I have always dumped the black tank first followed by the two grey tanks to flush the hose. I have always waited until they were very full before dumping and still a rotten smell inside the RV when I'm done.

Well, I'm glad to say that I have found the issue and my findings may help you. Apparently when I dump my tanks the exiting waste produces such a suction that the P-traps under the sinks and tub have the water sucked out of them and the smell rises through the now completely empty pipes.

Solved the problem by putting the drain plug in each sink and tub and filling up each with enough water to cover the plug. I then drain the tanks just as before and presto! NO SMELL.

Just a little nugget of info for a Sunday! y'all have a great day!

If you are getting that much negative pressure in the tank when you dump, it sounds to me like the tank vent may be clogged. What you are describing should not be happening.

It would be worth cleaning out the gray tank vents to see if that helps.

On my Cougar, the galley sink drains to its own gray tank. There is no vent to the roof. Instead, there is vent built into the drain plumbing underneath the kitchen sink. It's a one way vent that doesn't allow air from the tank to escape into the trailer. It's called an air-admittance-valve and looks something like this: http://www.oatey.com/regions/canada/...s/in-line-vent If this is damaged or defective, it will also cause the situation that you are describing.

[hankpage]

What you are doing is one solution but the cause is a blocked vent. Either a through the roof vent is blocked or a "cheater" vent under one of the cabinets is not working. I would suspect the cheater vent under your vanity and replace it. You will also find that your tanks will drain a little faster. JM2¢, Hank

[JoeofNSB]

I should have mentioned in the posting that I had checked the vents both on the roof and the two under the sinks. Definitely had clear vents as I could feel the suction while dumping. It had me baffled for a year now.

[hankpage]

Originally Posted by JoeofNSB

I should have mentioned in the posting that I had checked the vents both on the roof and the two under the sinks. Definitely had clear vents as I could feel the suction while dumping. It had me baffled for a year now.

The only way to test the mechanical vents under the sinks is to remove them and blow back through them. But if you go through the trouble of removing it, for $5 replace it and test the new one before installing it. (much more sanitary) They are all cheaply made and bad ones are common. I think you will find that one, or both, will be your stinker. Your p-traps should not drain while dumping.

[JRTJH]

Another consideration is that the roof vent on the black tank may extend into the black tank further than it should. If the "tank end" of the vent is covered with waste fluid when the dumping starts, it will create a vacuum in the tank and cause slow draining. Once the vent "tank end" is clear (as the tank empties) it will function normally. Getting on the roof to check the vent when the tank is empty will always give "normal" results. Checking when the tank is "as full as it gets" may produce a different finding.

Now, the black tank has no bearing on the gray tank dumping or on pulling water from the P traps. The gray water system is isolated from the black tank (as long as the gray tank valves are closed when dumping the black tank). So, pulling sewer gasses (black tank smell) into the coach when dumping the gray tanks shouldn't occur. If it does, then as stated, I'd just replace the two "cheater vents". There's one under the vanity for the front gray tank and one under the kitchen sink for the rear gray tank. Essentially the "cheater vent" is nothing more than a "gravity seal" latex disc that lays against a plastic seat. With age, the latex disc dries out and "wrinkles" (Why does that image seem painful???). Cheater vents tend to "age out" every few years and should be replaced when any increase in "plumbing smell" starts to occur under the sink or vanity.

[hankaye]

JoeofNSB, Howdy;

Originally Posted by JoeofNSB

I should have mentioned in the posting that I had checked the vents both on the roof and the two under the sinks. Definitely had clear vents as I could feel the suction while dumping. It had me baffled for a year now.

I have experienced the same thing, I ALSO checked my roof vents and
found them clear. I just dump 2 cups of water into the shower and the
vanity and poof no smell.
I guess when you see the exiting effluents back-up in the clear section,
that would most likely be when the suction becomes great enough to
suck out the traps. Wild guess I know, but, in my mind it's Ok ..."
As long as the smell goes away, I'm happy.

hankaye

[mikell]

We sometimes have issues when the unit rocks back and forth too much the shower seems to lose the water in the drain. Now the first thing we do is put water in all the drains when we stop.