Checking for potential gray tank/plumbing leak

[shawncberg]

On our last trip out an odor developed in our rig. It didn't smell like a black tank odor, but it was definitely strong enough for anyone that entered our rig to smell. It started in the rear bathroom, but eventually filled the entire rig. We use Happy Camper in our tanks religiously, but drained & flushed all of them thoroughly to make sure that wasn't the problem. We also aired out the rig afterwards, and as soon as we closed it back up the odor would re-appear. It seemed strongest in the pass-through storage, so I removed the carpeted wall to take a look around, and it definitely smelled more behind that wall. I crawled in the front there and looked around and didn't see any leaks, water or anything unusual. We let that air out a while with fans and again when we closed up the rig the odor came back. As a last resort, I went ahead and replaced all of the air admittance valves under all 3 sinks with Studor vents to rule those out. Again we aired it out, but after closing it back up the odor was back. We also checked the plumbing vents on the roof and they were clean and clear. We never did figure out what it was, but after we towed it home (only an hour) and parked it the odor was gone and hasn't come back since it's been stored for a few months (we check it regularly).

My only guess at this point is that maybe there is a gray tank crack or very small plumbing leak that is letting air/gasses escape and causing the odor. We never did see water underneath the rig or filling the underbelly, so if this is the case it either isn't leaking water (maybe a small crack at the top of a tank?) or it just isn't leaking enough to where we'd notice it.

I had a mobile tech come out who wasn't interested in pulling the entire underbelly down to inspect everything as he said we would've seen water somewhere if there truly was a leak, but I don't necessarily feel that's 100% true. If there's a crack near the top of a tank letting gasses escape and we never fill the tank it wouldn't leak any water.

In any case, I'm hoping someone here can give me some advice on how to troubleshoot this. I've never smelled a dead animal before, but I imagine if that was the case it would be much more pungent and also wouldn't have just disappeared after towing it home an hour. I guess it's possible a live animal got into the underbelly and was just hanging out down there causing the odor and he vacated when we were traveling home, but not 100% sure.

[ncitro]

shawncberg You've done some pretty thorough troubleshooting. The thing I was going to suggest was the AAV, so that's out. There's also sometimes a "duck bill"one way valve below three shower that acts as a p trap for the shower, I'd check and see if it's clear and functioning. If so then I'd look at the vent pipe itself if the smell comes back. It could be it's somehow cracked inside the wall or not seated properly in the tank?

[howson]

shawncberg -- not sure if this will help, but check out this thread: https://gdrvowners.com/forum/operati...antry-cabinets

[shawncberg]

shawncberg You've done some pretty thorough troubleshooting. The thing I was going to suggest was the AAV, so that's out. There's also sometimes a "duck bill"one way valve below three shower that acts as a p trap for the shower, I'd check and see if it's clear and functioning. If so then I'd look at the vent pipe itself if the smell comes back. It could be it's somehow cracked inside the wall or not seated properly in the tank?

That's a good idea. I'm debating on bringing it to a local campground for a week or two to use it and see if the odor comes back. Any tips on checking that vent pipe for cracks or proper seating inside the tank? I've also debated pulling the whole underbelly down and inspecting everything myself but it seems like it could be a large job to do that.

[shawncberg]

shawncberg -- not sure if this will help, but check out this thread: https://gdrvowners.com/forum/operati...antry-cabinets

Thanks for sharing this! That certainly could be a possibility. None of these mobiles techs want to drop the underbelly, so I think I'll have to do it an inspect it myself. Any tips for doing it alone? What I should look out for?

[ncitro]

That's a good idea. I'm debating on bringing it to a local campground for a week or two to use it and see if the odor comes back. Any tips on checking that vent pipe for cracks or proper seating inside the tank? I've also debated pulling the whole underbelly down and inspecting everything myself but it seems like it could be a large job to do that.

The vent actually connects to the top of the tank, so it's hard to get to. You could start by taking the false wall down in the pass through storage. There's a lot going on back there but you should be able to see where the vent lines go into the tank there.

[Cate&Rob]

shawncberg

x2 on Neil's advice that dropping the underbelly will not access the tank connections and drain/vent pipes which are above the tanks.

Contact Grand Design Customer Service with your VIN and ask for the holding tank drawing for your trailer. There is actually a pretty good drawing for the 311BHS . . . unfortunately, the moderators are not allowed to share these drawings . . . they must come from Grand Design to owner and it will be expect that you also will not share these drawings.

Behind the aft wall in the pass through, you will be able to access the drain and vent plumbing for the forward grey and black tanks. A place to start.

You might try putting something with a strong identifiable smell into each tank (one at a time) to try and identify which tank the smell is coming from.

Rob