If you have periods of non use, you can add various septic tank type bacteria products and let them do their work. Then, hopefully, take it to the dump station with a better result.
You can use our search feature to find the products available.
If your tank is just draining slowly, you might also try the old trick of ice in the tank. Just before hitting the road, make sure you've dumped and then added about 1/3 tank of fresh water to the tank. Dump a couple bags of ice cubes into the tank and drive around to have it slosh against the wall and dislodge stuck on "stuff".
Best of luck
Rick, Nancy, Peanut & Lola our Westie Dogs & Bailey the Sheltie.
2007 Itasca Ellipse 40FD