Since your going to be sitting in place for a few years, the primary objective in your situation should be to prevent solids accumulating in your trailers tanks, and the drain lines. You want to have, as much as possible, all the solids in both the gray and black tanks drain into the septic tank.
The best thing to do in your case would be to connect your trailer to the septic system using the same 4” PVC sewer pipe used on a house, and not the flexible hose “stinky slinky”. None of those hoses are intended to be left out continuously for years at a time. PVC has a smoother interior, and won’t trap solids as readily. It’s also more durable.
Then, use your trailers tanks in such a way that there is never a long, slow stream of water flowing through the drain pipe. That’s what happens if you leave the dump valves open on either tank. You should leave the valves closed until the tanks are filled to point where there will be sufficient volume released to flush the majority of the solids into the septic tank. How often you dump will depend on the size of the tanks, and how quickly they fill up, but I’d try to let them get at least half full.
When it’s time to dump, drain the black first, then the gray, so the gray water will help move any solids in the drain pipe into the septic tank. Since your trailer isn’t a park model, that’s how I would do it.
:):)
2001 Lance 1121 on a 2016 F450 ‘Scuse me while I whinge.
And for all you Scooby-Doo and Yosemite Sam types………..Let’s Go Brandon!!!