Roof Vents and Odor

[BigBoy2U]

I recently have had a bad black tank smell in my bathroom. I replaced the toilet a couple months ago and replaced the O ring also. The smell started and is really bad when it hot out. If I use the fans to pull air out of the unit I can fill the rig with the smell of the black tank. So I thought I would get up on the roof and check the vent(s). The first one I suspected was the one near the bathroom. I removed the cover to find it full of wasps. Killed them and removed the nest. But the pipe was still blocked I was shocked as I was sure I just cured my problem. I removed insulation. Then the ABS pipe just slipped out and I realized it was just vented into the attic. So this must be the vent for the bathroom fan. I replaced it and put a nice fiberglass screen glued to the top of the pipe to keep bee's out. So then I check the next closest vent and it really has no smell so I figure it must be the gray tank vent. But then I notice that way over by the passenger front near the closet area is another vent. I go check it and its also has a nice big wasp nest in it. So I kill and remove that. Only to find insulation again. I remove the ABS pipe and it only goes into the attic? What is this pipe for?

I then check what I thought was the gray tank vent. It was clear. I took a hose and ran water down it and had water coming out of both the black and gray tanks. Is there only one vent for both tanks?

Short of the O ring slipping up the toilet on install (Concerto) what else can cause that black tank stink? I don't have the smell in the basement and it only seems to be in the bathroom. 2005- 36TK3