Rinse out your RV holding tank and allow it to dry. You can use your normal post-trip procedures for doing this.
Locate the cracks on the RV holding tank. They should be fairly easy to see on the black PVC tank. They'll appear as light lines in the dark plastic.
Drill a small hole in either end of the crack with your cordless drill. This will alleviate any pressure that the cracked area is experiencing.
Rough up the surface with fine sandpaper and steel wool to prep it for the epoxy putty. Make sure surface is clean after sanding.
Apply epoxy putty to the crack using a spackle knife (a butter knife will also work). Make sure that you cover the crack from end to end, including the drill holes. You can find epoxy putty at most hardware stores or at an RV dealership.
Let the epoxy resin dry overnight.
Apply spray rubber over the epoxy to seal the bond tightly and prevent any condensation seepage. Cover over the epoxy with three to four coats and also do an inch to the outside around all sides of the crack. Make sure surface is free of any kind of dirt before applying the spray rubber.
