How do you reverse flush the vent line? Do you just push a hose over the vent?
That is exactly what I do. I stick a chunk of vinyl tube over the end of the garden hose and stick it over the vent while pumping out. Seems to do the trick, but just make sure everything is hose clamped! That said, if you really got a good hookup there is a risk of pressuring the holding tank and other associated fittings not normally under pressure so be careful.