Black tank level sensor

We just got back from a two week drip and had our first problems.  We waited until the black tank was 3/4 full and then flushed it.  We then ran the black water flush until the tank was 3/4 full again.  Still stuff coming out.  We did this three times until it appeared all clear.  Then days later after another cleaning we dropped an Oxy Chem clear tab and noticed that it got stuck and did not go all the way down.  I used a flashlight and could still see waste in the tank.  Filled it to 3/4 and rinsed a few times until it was flushing clear (we have a clear plastic elbow to see what is coming out). Although it looked clear, back at the toilet, using a flashlight there is still waste.  In addition, under the bath vanity was water and it was coming from a black relief valve which the dealer said was for the black water wash.  So something is not working.  We dropped the RPOD at the dealer on the way home for service.  Bottom line, I would use the black water flush after each dumping to help insure all is clean, don't just depend  on emptying the gray tank after the black as that only cleans the hose you attached.  It does not clean out the black tank. Also while the flush helps I think you need to occasionally clean out the tank from the toilet using one of those wands attached to a hose

BTW - to Toolman and Daniel,

I finally found issue to my backflush problem in tank and you folks are zactly right, a working system has a spray function, I have since restored mine to working condition. BLUFF is you folks where spot on. THANKS.

Thanks. I will ask the dealer to check if the backflush valve is backwards.

Originally posted by mcarter Richard Cindy, I went through some agony with my backflush. The valve was in backwards so I decided to move the backflush to drivers side. Rather than remove sink to fix valve. I like it much better on drivers side. Then I found previous owners had poked hole in the spray valve, probably because some genius figured it was plugged vice valve in backwards. Replaced spray head, and now have a functioning backflush with hose attachment next to the black water rain. No good deed goes unpunished:)

I have a 2015 178' and the flush is on the driver side from factory.. weird. Anyways to answer my original post, I ran a bunch of water into the flush valve without the drain open (just adding water to the tank), then drove to dump station. Dumped, flush and sensor works great! Thanks for all the replies

John, I looked at the level sensors from iconprocon and it looks like they needed to be mounted on the top of the tank, which can be a little complicated with many travel trailers.  I didn't see one that could be mounted to the side of the tank in tight quarters where the tanks are mounted very close to one another. Did I miss something?