Gray tank

[sfem192]

My fifth wheel is exactly like the OP’s and it used to stink when it was windy. The hole that was cut to vent the sink was much bigger than the pipe and was not sealed. I put sealant around the vent pipe and secured it where it could not move and it took care of the odors getting into the trailer. It was not hard to seal the pipe and I don’t notice any smell under the awning.

[WDPatterson]

Our 2004 Laredo has the screw on vent under the sink. At some point, it began overflowing on the floor under the cabinet. I screwed that thing shut, and I haven't had another problem since. No problem with burping, no hydrolock, everything works just fine. I look at a cheap valve like that as another failure mode.