We recently got back from a trip where I thoroughly flushed, multiple times, both black and gray water holding tanks before we left - both sensors read empty. after we got home I checked again and both tanks now read 1/2 full.
Do a search under "Tank Sensors" & you'll find 166 posts about them. Historically RVs have had inaccurate tank sensor systems (those with internal sensors). Upgrading to a newer external sensor systems like SeeLevel is a definite improvement.
Another problem is in the cleaning of your tanks (& their internal sensors). Everyone has their own ideas of what is best. Personally I use the GEO method occasionally, back flush with a "Flush King" periodically & always use a lot of water.
Ditto on SeeLevel being an improvement. They are not cheap, but the system is good and tech support is very helpful.
88 Gulf Stream 34' Sun Vista, Ford 460, Edelbrock Perfomer carb, Thorley headers
Ford F-250 crew cab 4X4, 6.0 turbo diesel complete roof rebuild
daughter 14, son 10
US Army Desert Storm vets (both of us)
left: The Ol' Gal right: DW with White Lightnin'
The tank walls get crudded up with stuff that contains water and fools the sensors. If your RV sets unused for a while the crud dries out and the sensors will read properly - until they get wet again. The key is to get the tank walls clean and that can be very difficult.
I have put a pressure washing wand down through the toilet and cleaned the tank wall where the sensors are. I got accurate readings for a while and then the walls crudded up again.
I do have a non-contact sensor system but the walls can get crudded up enough to fool it.
I have tried the "Geo" method and it didn't work for me. I don't have a tank flushing system and don't intend to install one. As a full timer I don't want to expend the effort to flush all the time.
I know that I need to dump the black tank every 12 days or so. I mark the calendar and go by that. About three days before I need to dump, I close the grey water valve so I have water to flush the hose after the black tank is dumped.
Clay (WA5NMR), Lee,(Wife) Codi, Brandi (Shelties) and Damncat (damn cat)
Full Timing in a 2004 Winnebago Sightseer 35N, Workhorse chassis, Honda Accord toad
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