We've had excellent luck with the FlushKing. I like backfilling after dumping till the runoff is clear. We've had ours now for 9 years and it is still going strong. All I have to do is spray the valve a couple of times a year to keep is moving smoothly.
Alfred
2005 Sightseer with Workhorse, ReadyBrute Elite towing 2003 Honda CRV
Map below shows states where we actually camped.....