If you have the black and the gray water discharge at the same outlet:
...you can back flush the gray water into the black tank and then dump the black tank, which will pull a LOT of stuff out.
In my photo "B" is the Black Tank valve.
C is the Gray tank valve.
A is 3rd valve (Flush King style) that has a clear section.
Steps:
1. Dump black tank first... completely till it stops (Open A and B). You can see it in the clear section of the valve.
2. Close Valve A. Leave B open and now open C. This will allow the gray water to back flush into the black tank.
3. Leave C open for about 10 seconds and then close it.
4. Now open A and B again. (This will redrain the black tank pulling a BUNCH more out.
5. Repeat a total of 3 times. After the third time, close the black tank and let the gray go, washing down the sewer hose.
Of course, this works best when the gray tank is full, or near full so there is plenty of water to swish backwards into the black tank.
This process works if you are dumping at the dump station, attached to a full hook-up, or using a sewer tote. I do this every dump, and it keep the black tank cleaned out. My trailer has the black tank flusher, and I also have the sleeve that goes into the toilet, and a wand that can go into the black tank via the toilet. But I have found the back-flush method does the best.
Actually, as a last step, put a little water in the black tank and drive onward. The little water in there will continue to slosh around, beating anything that might be stuck to the sensors, and pulverizing any solids that might have stuck. A few squirts of Dawn Dishwashing liquid will also help wash the inside of the tank too when sloshed around driving.
