Depends on how it was manufactured. I was in a campground a few weeks ago and saw a guy open the basement door and create a waterfall. Apparently some grey tanks have vents in the basement and are not vented through to the roof. I didn't know you could do this, but according to a couple RV repair Tech's I talked to they said they see it all the time, is ok since it is grey and not black, and the vent is lower than the shower drain, so it may not come up through the shower.
Disgusting! I wouldn't want gray water in my cubbies/basement. GW stinks almost as bad as black water.
A fast and cheap way to fix black tank sensors. ICE. yes I said ice. Dump 5lbs of ice down the toilet with a cup of bleach. Add 10 gallons of water and hook up. I try and hit as many bumps as I can. Then head to the nearest dump site. Drain the black tank. The ice acts like a scrubber.
Depends on the tank capacities on your rig. Depends on how many people are in the rig. Also depends on full hook ups or partial/no hook ups. You'll get to know your rig's capacity from using it and how long you can generally go before you need a dump station or to pull the handle on the black tank.
If we have water and electric but no sewer hookup, I usually fill the fresh water tank and work off of the pump. I have a clear view of my fresh water tank. When thats down, its time to dump.
With full hookups we keep the black tank closed and I pull the black water handle every 4 or 5 days.
Either way, make sure you use plenty of water through the black tank. In other words, flush frequently, cause the first time you gotta go fishing in your toilet to unclog the blockage , that definitely will get your attention. Use alot of water in the toilet.
When we have no sewer, the toilet is for emergencies and middle of the night visits. Fresh water is for the kitchen and bathroom sink. Washing dishes, hands etc.
Our sensors stopped working back in 04. (with exception of the propane)
Nothing we tried in the toilet worked to clean them. I've thought about new sensors, but don't really need them or use them.
After a few trips you should have a idea if the sensors are working or not. The a problem only arises when you have access to water but not sewer. If you are using your water tank then you know how much water has been used. In smaller RVs your fresh water is about equal to the black and grey tanks which means you can't over flow unless you use more than one tank of fresh water and use either the black or grey more than the other.
Mike & Dava
2007 Sierra Classic 2500 HD Duramax/Allison 4X4 Crewcab, Super Springs
2005 Carriage Compass 30RLS, MOR/ryde suspension & Pinbox, Onan 3600LP
Huskey 16K EZ Roller, DigiTrac