I think the first order of business is to clean out what you have now so you can use the flashlight and see what is really going on. Some trailers the toilet drops straight into the tank, on others there is a 45 degree bend between the toilet and the tank.
Do be aware that the tank itself may be fairly shallow. My Jayco has a 36 gallon black tank and it's only 5 inches deep in the corner where the toilet drops in. I think the deepest spot is at the drain pipe and it's only about 8 inches there. So you might be looking at the bottom of the tank and not realize it. In that case you need more water with the flush. Never flush a poop without having the toilet bowl full of water. Some people follow up with a second bowl of water, but I don't.
