a. If there are bubbles coming back, that suggests a clogged vent. If they don't have a way to get out, no joker valve will stop them. Blow it back into the tank with a water
hose. A failed valve will NOT cause bubbles, since the gases will go up and out the vent.
b. We're all assuming the hose dumps into the top of the tank. Thus, the waste is just in the hose. Flush enough strokes to move the waste all the way to the tank, then a few more to blow most of the clean water
through. There should be little waste in the hose. This is different than flushing
a home toilet; when the bowl is MT you are not finished. I believe this is explained in the instructions... which we all read, right?
c. Use a Raritan
PHII joker valve. It fits perfectly in your Dometic manual head
and last 2-3 times longer.