We typically stay at least 2 weeks at a time. Where we have no services, obviously both stay closed the whole time, no problem with black capacity, but we are forced to eat out a lot and use campground showers as the grey fills too fast.
In FL we have full services and stay 30-60 days. Here we dump black about every two weeks and leave the grey open until a day before we disconnect. Sewer gas? Not a problem, it just vents out the stack. Flies? Never noticed a problem. We do have a flush connection on the black tank that really helps when we dump.
I have a clear section in the bay and am surprised how clear the grey water is when I dump it. Still stinky though.
Ole and Anne Anderson, Highland, Michigan
'02 Adventurer 32V, Ford F-53, ours since 4/08,Goodyears, Konis, SeeLevel, CHF
'84 CJ-7 , 5.3 Chevy, 3" lift, 33's, Detroit Locker, Fiberglas tub, winch, hi-lift