I find the galley tank is a tough one. I think all the food bits and grease build-up and soap scum mess the sensors up easily. We even have the outside the tank SeeLevel sensors and they can't deal with it.
I have given up worrying about it since it's the last tank of ours to get full. If it's full, then we are headed to the dump station anyway.
In the past, I have undone the galley drain pipe and fed a hose down, and flushed to get the sensors working. I made them work for a time, but they fouled again soon enough, and that is a hassle to do all the time. Cheers, Ray

We often leave our Grey galley and shower tanks closed, especially if we sit for any length of time. That way when we dump the tank, the big “whoosh” will drag much of that crud from the tank. When we travel, we make sure there is water in all 3 tanks and we dump in about a cup of blue Dawn dish soap. The yuck that comes out after travel is amazing!

Good tips, I have always left all my tank valves closed until they are mostly full. I think if they are left open it's just a path for sewer gases and whatnot like rats and bugs to come up into the tanks. Plus the waste particles that aren't in the trickling water flow area can dry out in the tank and build up over time. Sewer gases can leak out the roof vents stinking up the campground. I have heard some will put a bend in the sewer hose to make a P-trap but then the flow is restricted, and like you say a good whoosh is a good thing!

we always leave valves closed too. When we start travelling again I will pit Dawn in tanks as you suggest. Are you puttingn1 cup into each tank.

Are you putting down 8 oz. in each tank? How much water?
Thanks for the tip

we put about 1 cup of blue Dawn in each tank. We probably have about 5 gallons in the black and a shower or two in the one grey and two or 3 dish sink fills in the galley. Enough to allow a good sloshing

Thank you!

We are only out for a week at a time but I have found even if the campground we are stay has a dump, we come home and dump at our public dump station along the interstate. The trip home and nearly full tanks seems to grind up and clean things so we have had good luck with Sea Level sensors and Happy Camper each dump.

When I travel I mix dawn and a dishwasher pod in a warm bucket of water so it can sloosh around my tank, both black and grey. This seems to keep the sensors working but they will stop working once you stop for any amount of time.

Are the Sea Level sensors worth the time and money if they stop working too?

My Seelevel are hopeless for my kitchen and black tank but work well for the shower and freshwater. Since they are the most important when boondocking, The shower always fills first for us I think they are worth it. But in hindsight, I'd only install the 2 sensors vs 4 and save money.
If I was to always be cleaning the black and kitchen tanks they would work but not worth my time. The kitchen is always last to fill up and the black I can tell just by the sound of the flush

For a number of years my grey and black tanks always read 1/3 to 2/3 full. I finally used a bunch of automatic dish washer gel (two cups or so) in the grey tank and some heavy duty enzyme in the RV black tank and let them set for awhile while mostly full.

I have been using my septic tank cleanout at home for a dump station instead of having to fight in line at the local campgrounds (short weekly stays). With the agitation in the tanks it really helps break loose the hard crusty buildup (you can see the chunks while cleaning the sewer hoses)

This probably hurt my fuel mileage , driving with fullish tanks and I have been told that this buts a lot of strain on the tanks themselves, but for the first time when I dump my tanks, both say empty.

One black tank option, which I realize will make some folks cringe, is to never flush TP down the toilet. If you've traveled much outside N America, you'll know this is actually the prevailing practice in many regions of the world. Smaller European towns e.g. have been relying on ancient sewer lines for many (many!) decades now, yet a visit to the bathroom in a restaurant or bar will almost always lack any particular odor. TP is simply placed in a small basket or container that has a lid. (Obviously, we use a plastic liner in our can and it simply goes away when emptying the main trailer trash. I can't say that's specifically why we've never had a black tank sensor problem...but I can say we've never had a weak flush at a pump out station. A related suggestion: I measured the amount of water it took to activate each sensor in each tank using a little flow meter on the end of a hose. Gosh, those sensors were off! Our 45 gal. black tank sensor changes from 'Empty' to '1/3 full' after the first 2.5 gals of fill. Each tank's set of sensors are different from the others; so I've found it helpful to have done this. FWIW we've never used an additive in either the black or grey tank. WRT our grey tank, we leave a small Oxo rubberized screen in the drain of the kitchen sink, where it inevitably catches food particles. That's probably a very common practice.

In 2 RVs we've had in recent years this has always been a problem

The only thing that I've found that works for us was Thetford tank blaster. We had sensor issues on both the grey and black tanks on both our fifth wheel and our motorhome and that did the trick.

It comes in a 4 pack (i believe) on Amazon, perfect for treating an "average" RV - 2 packs for black and 2 for grey. Drop in the packs around dinner time fill your tanks and by morning they're clean.

Now, as much of a pain as it is, I don't leave our grey tank open. I go out every couple days to drain it.

I tried the vinegar Calgon treatment and it didn’t work either.

Has anyone tried a borescope to get a look at the sensors?

John

Looking at the Rhino Blaster Pro, w/Gate Valve, seems like it might do a better job of cleaning the tanks. We already have the gate valve that allows us to equalize the tanks, it would stay open using the rhino blaster.

Has anyone tried it?

John

I'd try emptying the tank, filling it with about 1/4 to 1/3 tank of clean fresh water and dump 1/2 gallon of vinegar down the drain. Do this when you're leaving one site for another; you'll need the sloshing around to clean the whole tank. Don't leave the vinegar in the tank longer than hours for sure. See if that works for you.

Will try vinegar. We just drove from Vancouver to Calgary, first trip since Covid started. I think it was good just moving. Big improvement.