There is an ABS glue that works on wet or dry fittings. Empty the water from the under belly using a bucket, 1/4" drill. Pull your gray water valve handle and tip your rig towards the drain side. When fully drained tip it back the other way. Drill by hand and fill the bucket 1/2 way and plug the hole with the smooth end of the drill. Repeat until the under belly is empty of water. You will have to cut the Coroplast. You can patch it back up using Gorilla Tape. Just make sure you clean it well. Then check out the plastic fittings that have the clamps on them. If loose, glue them with ABS cement and not PVC cement. If they are glued and leak then you have to cut them out and out in new plumbing pieces. If a flush cut is necessary and it happens to be leaving a pipe and outer coupling sleeve from a fitting, a "PIPE HOG" can be used with a drill to remove the inner pipe so a new connection can be made. All things are fixable. Drain plumbing is the easiest, but a real pain sometimes to do.