All of my many years RV experience has been with bomb drop toilets. I have always abided by the procedure of keeping the black valve closed until ready to dump with at least half a tank.
I was asked for advice by a lady with an sob coach which has vacuum flush system about whether to leave both the gray and black valves open full time or keep the black valve closed until half full or more. My first reaction was to advise to do as I have always done. After thinking about it I realized that maybe the vacuum systems are different.
So my question for those with experience; Is it normally acceptable to leave the black valve open full time if you have vacuum toilets?
Thanks
We have the Sealand, (Dometic) VG2 vacuum generator toilet setup. We don't leave any waste valves open until dump time. I don't think there is any requirement to have the waste valves open. The VG unit is a separate subsystem, once waste is evacuated from the toilet and cassette it's deposited into the black tank.I assume the black tank is vented, as we've had no issues with pressure buildup with waste valves closed in use.
I believe there is an advantage to allowing the tanks to fill up. We have the third Valterra waste valve installed and use it to backflush the black tank with the gray water tank. This allows you to flush more of the solids from the black tanks.
It works great, does need to have preventive maintenace performed about every 2-3 years, replace the four duckbill valves and the toilet ball seal.
Jeff
Why does the term "vacuum toilet" system bring to mind the image of the vacuum canister delivery system at our bank driveup?
Vacuum toilet systems are popular on large yachts with holding tanks. To complicated imo. And costly.
Because it is exactly the same system! Took me YEARS of dealing with the Sealand Magnum Opus Turbo Turd 3000 and it's extravagant circuit board and extenuating issues before I finally found a guy who knew what he was talking about. The vacuum system is not an issue if you keep the maintenance up. We always ran off the onboard water tank. When you need to fill fresh water, then dump the tanks. Backflush the black with the grey, use the tank flush to rinse, and Bob's your uncle. I never used any tank chemicals except a good glug of white vinegar in each empty tank.
On our 2003 U320, the black and grey tank both share one roof top vent (verified myself).
The black tank dump valve must be closed until dumping, or a pyramid of solids will accumulate.
Geez Carol!! Now my crazy imagination sees those vacuum canisters at the bank going back and forth full of brown "stuff"!! :))
See thread titled "black tank clogged".