Smell in camper when emptying tanks and flushing

[60sumtin]

Originally Posted by Rickho

I never saw the smell as a venting issue. When I dump some smell does come in and has since it was new. Doesn’t the act of dumping cause a vacuum effect pulling air away from the venting? I would only be concerned if it was a constant smell under normal use which means you have blockage.
When I dump I open the bathroom sky light and turn on the exhaust fan to draw residual odor straight up and out.
When done I give the tank a thorough flush with the hose used only for the tanks and add 1/3 water back in to keep it functioning properly.

Yes, when dumping there is a vacuum created in the tanks. As the water drains, outside air is drawn into the tank via the vent. If the vent wasn't there or blocked the created vacuum draws air through the sink and tub drains. When that happens the water in the p-trap also gets sucked out and into the tank allowing tank odors to enter the RV. The p-trap stops tank and sewer odors from coming up through the drains. Conversely, as the tank re-fills air that was in tank is pushed up and out the vent. Without a vent that air would have come up through the sinks and tub and into the the RV. A proper working vent system should be odor free.

[BFlinn181]

Originally Posted by 60sumtin

Yes, when dumping there is a vacuum created in the tanks. As the water drains, outside air is drawn into the tank via the vent. If the vent wasn't there or blocked the created vacuum draws air through the sink and tub drains. When that happens the water in the p-trap also gets sucked out and into the tank allowing tank odors to enter the RV. The p-trap stops tank and sewer odors from coming up through the drains. Conversely, as the tank re-fills air that was in tank is pushed up and out the vent. Without a vent that air would have come up through the sinks and tub and into the the RV. A proper working vent system should be odor free.

The purpose of the AAV is to prevent the emptying of the water in the P-traps. If the AAV has failed to prevent draining of the P-trap, then a 2 second running of the faucet will refill them. Most often black tank odor will be allowed into the RV by a toilet seal not holding water in the bowl.

[Spk64]

If your roof was just replaced I would closely check the vent stacks on the roof. Make sure they are open and clear as others suggested. The other problem area is the penetration through the roof. If the pipe is not fully sealed you may get some odors drawn back in under the ceiling which then may come out anywhere inside. If you have vent caps may need to remove them to see if a problem exist.
It does seem odd that an odor is escaping when dumping as the roof vent is pulling air in at that point and not pushing air out.

[60sumtin]

Originally Posted by BFlinn181

The purpose of the AAV is to prevent the emptying of the water in the P-traps. If the AAV has failed to prevent draining of the P-trap, then a 2 second running of the faucet will refill them. Most often black tank odor will be allowed into the RV by a toilet seal not holding water in the bowl.

Exactly, assuming the AAV is working properly but after dumping not everyone thinks of running the faucets to refill the traps. A failed AAV dumps tank odors into the RV, not to the outside atmosphere like a normal roof venting system does.

Failed toilet seals are a different matter. If the toilet bowl holds water there's an air tight seal.

[daka320]

Had the almost same problem. Unscrewed the one way pipe vents and capped them under the bathroom sink and kitchen sink. No more smell. No problems with filling or dumping tanks. Problem solved.

[54Fun]

Thanks guys...OP here. As much as I replaced the AAVs previously ($6/each at Lowes)...I just picked up 2 Oatey's ($13 each at Home Depot)...so, hopefully those will eliminate any issue (if there is one there). I'll also get up on the roof tomorrow and make sure the roof vents are operating properly (good point above on when the roof was replaced - that is kind of when these problems started)...I got a snake to make sure nothing in there...

Another issue (replaced maybe)....this happened a few weeks back...my underbelly tore away from the frame and was getting filled with water... my guess is that it is my gray tank overflow....what would that point to? is it some funky smelling water as well, and smell from it gets sucked up my my MaxxAir fan into the coach... any thoughts on how that is related?

[BFlinn181]

Grey tanks don't usually have an 'overflow' it just backs up until it shows in your lowest drain. If the underbelly is made of a material that can absorb water, that might be the source of the smell. Be careful dropping the snake down the vent, you don't want to damage the tank below.

[54Fun]

Well, it turns out that my tub drain....the horizontal slip joint after the P-trap never (I think) had a gasket in it...so when the gray tank would fill, or when someone would shower, that thing was gushing the water right into the underbelly. So I bought a whole new P-trap and drain assembly (I'm no plumber, and ran into several issues, but eventually got it fixed - and cleaned up a huge amount of hair leading into the trap)... so I had to cut an area of the underbelly to drain out probably 30 gallons of water that was just sitting in there, then sealed it back up. So I'm "guessing"....the odors were just coming out of that slip joint since it was not airtight...then probably sucking the p-trap dry with it?

I want to get back into the underbelly and clean it with some solution, dry it out, then seal it back up. Any ideas what to use? I thought about the black tank solution many folks use of calgon & Dawn + water?

I still haven't tackled the fresh tank issue...sounds like I need to replace the check valve there...

[Rickho]

How long has that water been sitting under there? Months/years?
Hope it didn’t cause rot to anything else. Poor workmanship...

[54Fun]

Originally Posted by Rickho

How long has that water been sitting under there? Months/years?
Hope it didn’t cause rot to anything else. Poor workmanship...

Poor workmanship for sure. As far as I can tell, the water only landed directly under the plumbing, on the plastic corrugated underbelly, so I don't believe there will be any issues with mold or rot. I believe I just need to clean the underbelly from the gray water sitting on it

[Rickho]

That’s very good indeed.