[DutchmenSport]

Why not just hook up a 3rd valve, like a Flush King on your tank outlet and simply back flush the grey water tank into the black water tank and flush out the black tank. It takes NO more water and flushes out the black tank very well. If the grey tank is full, you can back flush 3 or maybe even 4 times. The last back flush, simply close off the black tank and leave the water instead of adding even more water. Then use the remaining bit of grey water to flush out the sewer hose.

Back flushing does not use any additional water, you can do it even if you have no additional water source, and you are recycling your grey water for another purpose, a useful purpose.

If you back flush every time you dump the black tank, the black tank does not get any build-up in it. I have a black tank flusher, and very, very seldom ever use it because the back flush works so well.

Water conversation is one of those areas of responsibility that we all need to consider as avid RVers.