ive always been told DONT open the toilet room roof vent (unless the fan is running)....as it could circulate fumes between the toilet room & the vent pipe
i think if the fumes were passing thru the water, youd see bubbles.
i recently discovered (w/ a pretty full black water tank) that the infiltration of sewer gas was possible, when driving down the road....basically our tank was 3/4 or more full and i was unable to find a dump station....i guess the sloshing around agitated the tank and cause some sewer gas escapement. generally on road trips our tank is pretty empty...usually not more than 1/2 full at best so weve never had an odor issue before.
a few months ago i re-built our toilet (since the blade seal was leaking a little) i replaced all seals, added a sprayer (worthless, since you have to have your foot on valve/open to use it) and i even added the 2 inch riser.
'04 Haulmark (M42386) 42', 2 slide, 10kw - Pictures
'04 F350 CrewCab Longbed 4x4, 50g aux tank & gear vendors dbl over