I have a better way, IN fact 2 of 'em
First the OEM flush device on my RV was SELF WINTERIZING. Yup there is a Vacuum breaker mounted ABOVE the tank somewhere in the RV. with no pressure in the line this allows water to drain eitehr
Inlet to breaker, , back out the inlet
Breaker to Black tank.. into the tank.
At this point you are winterized, no need to do anything. PERIOD, and it worked just fine the first year that way
Next method. Compressed air.. Blow the water into the black tank. Then dump.
FInal method (THe one I use now and by far the best) I go south for the winter.
