We just de-winterized our trailer and checked everywhere for leaks. We bought this trailer in January and we were not able to test the plumbing system until now. We found that there is a leak behind the toilet only when it's flushed. The leak seems to be around the area where the Phillips head screw and the black part is. I'm not sure what that part is for. The area behind the toilet is so tight, I'm afraid I'll have to take up the toilet to find out where the leak is and how to fix it. Can anyone help?