Hi Tony - the access for the dump valves should be in the front storage compartment right behind the back wall. With one of the back wall panels removed you should be able to access everything for the dump valves, as well as the water pump and furnace.
I didn’t have a picture handy to show the actual valve, but they’re easily identified since there is a big cutout in the flooring to access them. There’s a small “grenade” pin that attaches to the valve handle and if that has come off, then you’ll hear the actuator running, but the valve won’t open. You can manually open the valve too in an emergency from here too.
This thread has some more details on the actual valve that should help too.
Hope this helps.