Black Tank Flush Problem

[Canada Goose]

I have a new 2104 355RK Avalanche. When I attempt to flush black tank I just build up pressure in the flush line. I do have the black tank valve open.

It has been suggested in a phone conversation with my dealer that the check valve in the flush line may have been installed backwards. Anyone else have this issue?

[Ron]

There are a few folks on here that had the same problem and yes the vacuum breaker is probably installed backwards...while it is out you may want to upgrade to a brass one that is a lot heavier, there have been a lot of issues with them leaking or of course breaking if not winterized properly...