A friend was told this by a Jayco mechanic. At the end of the season when you want to clean out your black tank . Dump a big bag of ice cubes before traveling it will swish around while moving and remove stubborn remnants. When you get to the camp ground dump the melted ice. I use mine for hunting late season so I will try this , just thought I would share.
I, like AVVIDCLIF, use the built in flush system with a clear elbow between the outlet and the hose. One thing I've noticed is that when the water runs clear is that the tank is not necessarily empty. I close the dump valve and put in a bunch more water and dump it again with the flush off. Once the tank is empty I turn on the flush and usually see more "stuff" come out. I repeat the process several more times until I see nothing but crystal clear water coming out.It doesn't necessarily get the sensor clean but the tank sure is.
I've used the ice cubes before and they do help especially if your tank hasn't been flushed well in the past. And I have seen some improvements on the probe but it's hit and miss.
I have used the ice cube trick and was amazed how well it worked.
I had dumped, rinsed, and dumped a second time at the end of a camping trip. Thinking the tank was pretty clean, I thought I would see if the ice would do anything. Put a bag in the empty tank and drove home. I decided to use a bucket to drain the melted ice and I was amazed at what came out into the bucket.