This is how I did it.
I bought a drain and cut a hole in the bottom of the portable toilet with clear window caulking I sealed it and screwed the two together,I then cut a hole in the bottom of the trailer and used a elbow and a screw on cap on the end.
I have a hose from the outside I use to fill my tank and I can flush the toilet out from the inside.
I had my water tank where I have the toilet is now so I moved it to a better place and now.
this photo is how it is now.
I filled the portable toilet with water and it drained out perfectly,now I don't have to empty the toilet like I did before.
Bottom of the portable toilet where I sealed the drain.