Flush won't take water

[Cosmopolitan]

Cleaned out the sewer yesterday, opened the black tank, then the grey. Hooked up water to the flush turned it on. No water will come out, can't even hear it running. Went into my 2020 Greyhawk motorhome and no water even going into the black tank.. We've dumped it numerous times and flushed it. Can't figure out what to do.

[JFlightRisk]

The check valve may be stuck. It'll probably be just behind the screen/washer where you connect the hose. If you remove the washer with the cone shaped screen, you should see it if it's located there.