I think if it were me having a problem like originally described I would probably do the following:
1. My PC has a cover on the big hose dump port and on that cover is a regular garden hose connection with a cap.
2. I would take one of my old (I have a couple of used ones I keep for various uses) washing machine hoses (they have female hose couplers on both ends) and attach to that dump port at the hose connection, leaving the cover in place.
3. I would then hook up my garden hose to the free end of the washer hose. I would also have my standard 40 pound rv hose regulator hooked up to the garden hose.
4. I would make sure both the black and grey tank valves were closed and I would turn on the 40 psi fresh water hose, forcing a back pressure into the macerator pump which would already be turned on and see what came out, if anything.
5. If nothing came out, I would know the problem was probably in the pump or right at the pump.
6. If she no go, I would disassemble the pump. I am reluctant to mess with my pump because I have had lots of problems with the way PC mounted it and I have pretty successfully remounted it to better align with the rigid pvc from the tanks. Essentially, road vibrations would cause the bayonet to pop a leg and I would have to replace it as I recall. I modified it soon after I got it ten years ago last month and it is storage now so I can't recall in detail just what all I did to elevate the problem.
