there are two small vents on the roof, but i had long been suspecting that they were deaf ears, as i had never smelled bad odor from there. finally i proved it yesterday, in an unpleasant way.
at a dump station, after emptied the black tank, i was adding water through the rinse port. in about 10 minutes, i heard a whistle sound from the restroom. i went and noticed air bubbles arising from the bottom of standing water in the toilet. without thought much, i stepped on the release lever. boom! the water was splashing out. what a mess!! i spent hours to mop again and again wherever it could reach. fortunately while being unfortunate, at least it was NOT yellowish
the pressure built up to that high tells me that the vent was totally sealed/blocked. it couldn't be true that an object was dropped into the vent to have that effect. what could it be? i suspect the tank maker had never punched through the wall at the port (similarly the punch you would need to do on a kitchen waste disposer when you install it) and the installer in cc didn't bother to look at it.
from the upper access door in the hurricane heater compartment, i saw a 1.5" dia. black rubber hose clamped on to a terminal on the top surface at the corner of the black tank. i will try to disconnect the hose and check if there is a hole in it. i don't see a hose for grey tank from that access though.
what do you think? any experience or comments?