Leaky Dometic toilet water intake valve

The toilet intake valve leaks with the on board pump pressure as well as our house well pump pressure of 60 lbs, doesn’t appear to be a way to take the valve apart to see what the problem really is either. I sanitized and flushed the camper water system, putting in another new valve as well as a cut off valve in the line as a backup for the problem, on the new valve I can see a screen in intake so what ever gets by the screen would be pretty fine.

Does the most recent one leak?

So the replacement valve doesn't work any better and it still leaks under pump pressure. It sounds like there is some kind of debris in the water system that is getting stuck in the valve. Either that or when you installed the new valve you did not get it seated correctly.
since I'm guessing you have debris in the valve I doubt a Thetford would work any better.

Do you possibly have enough hose length to disconnect the fill pipe from the valve, wrap it in a coffee filter and put it in a dry bucket. Have someone turn on the water pump while you hold the hose end in the bucket. Count to 30 and turn the pump back off. Now check the coffee filter and see if there is debris stuck in it.

The Dometic 310 is far far better than any Thetaford toilet .. ever..

Since yo7 have replaced the flush valve I would look at the pedal assy to see if it is binding up when the toilet foot pedal is pressed down to flush the toilet..

If either the foot pedal is sticking on the side OR the inside bowl seal or flush port is sticking then it will not let the pedal return t9 proper position and will keep the plunger on the flush valve partially depressed..hence the flow of water