Originally Posted by jornvango
The manual differentiates a check valve and a gate valve.
I assume the gate valve is the sewage valve, operated when dumping the black tank contents.
See attached picture.
Where is the check valve and goes one usually leave that opened?
The check valve is automatic, usually internally spring loaded. Water pressure overrides the spring pressure letting water flow.
The Vacuum break is also to be checked. It's purpose is to ensure water drains from lines so there is no water there during freezing temps.
Last, the nozzle itself may be clogged.
These parts are accessed from underneath the AS. You need an access panel to service them.
On out 1999 Excella it looks like this