We have always battled a faint black tank odor around our front bathroom since new. I had changed the toilet base gasket, Air Admittance valve under the sink, which was bad, but driving in certain wind directions or boondocking after about 7-10 day, we would smell it. Well others have found open gaps around their roof vent pipes and roof panels so thought I would check……now I know where it was coming from. The vent cap is a 2 piece, base and cap. The vent pipe should stick up through the base, providing a decent seal, and then the cap screws on. 3 out of 4 vents were correct with the pipe sticking through the base but the vent for the front black tank was cut to short, leaving about a 3/16” gap and then once the base was removed, I found a very oversized hole was never sealed. Now it gets even better, when they drilled the hole in the roof, they drilled through the AC ductwork, both the grey and black vents were drilled through the ductwork. So at times, we were getting sewer gas seeping into our AC ductwork causing the smell and making it hard to pinpoint. Foam was an easy solution for the gap but didn’t want it going into the AC ducting so I used some Dollar Store cutting mat material and fit it down around the duct cutout and vent pipe, then foamed it in sealing it all off. I then installed a better vent cap, using the Lippert 360 siphon cap……hopefully we will finally be rid of that faint smell that I always though was from my wife.
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