Hello all, I am a brand new member and needed some help figuring out how some things work on a travel trailer.I just bought a slightly used 2017 34 ft Nomad with a slide.I am using it a place that has a city water hook up and a septic tank...So this weekend I hooked it up for the first time.I put the water line into the t.t. ,attached the sewer hose and pulled open the handles for grey water and black water and assumed I was good to go.With in a few minutes it appeared that most of the freshwater I was putting in was coming right back out of the sewer hose..So I closed the black water valve and the water stopped coming out of the sewage hose....THEN, water started shooting out of the toilet, fortunately it was all clean water,but I immediately open back the black water valve and it all drained off and quit overflowing..so the question is what am I doing wrong?Should I not have a constant water source running all the time to the trailer or am I missing a valve that needs to be open or closed?I am brand new to this and appreciate any feedback.