Originally Posted by KamperKen1967
Yes the black tank valve must be open... but gray needs to be closed or can back up using tank cleaner
I think you're referring to when the black tank is draining, right?
Even if it did back up some, you're going to flush it right back out when you dump the grey water tank.
Always dump grey water last anyway.
Just got back from a trip and I got me a rhythm going with the black tank flusher.
I set an alarm on my phone for 2 mins, dump the black tank, snooze the alarm, alarms again in 2 mins, rinse, repeat, until all is clear.
Allowed no more than 2 mins to fill. I didn't want another problem.