Are you sure you want to find a cure ???
Go buy your self a clear plastic outlet that hooks up to your trailers dump outlet, and your sewer hose to it. (elbow or straight) Also at that same time buy a tank inserted cleaning wan that you hook up with a hose and has a shut off valve on it's handle. With a anti-back flow valve at hook up. Have some one open the water hose valve to your wan full blast out side. Leave the trailers valve closed and insert the wan into the tank paying close attention to spraying as close to the bottom as possible to began with, letting the water beat against the bottom and its parts. As the water starts to fill leave the wan near bottom to create a swirling motion in the tanks water. Run the water until you believe the tanks is 1/2 full or a little more. Shut your water off and have some one pull the release valve on the trailer and watch the color of the water as it exists threw the clear plastic. It going to have a brown color. Now if you would give it some though,,, clean tanks have no odor.
Second go around, if the chunks are still flowing ,repeat the above several times until none. NOW, as you have used the tank in your past adventures, the brown water has built a scum line up the sides of your tank, of guess what. So if you have dumped, and in you next voyages the water has not raised to this previous level. That scum line is still there. Now is the time to attack that line , use a up and down motion with that wan to clean the sides of that tank. Until the water flows clean there at your newel bought clear site gage.
Repeat brand new, OR ,,clean tanks just do stink, Poo does stink,,,, there for,,, odor = poo some where in the tank. Repeat to your self,, poo equals stink. poo=stink, poo=,,,,,.