That picture makes it kinda hard to see the actual hole, due to all the paint shop work, but i'm guessing the hole is roughly the size of a nickle or so? If it's in the base of the bong where the water goes, you should be totally safe using some water resistant modeling glue, or super glue or gorilla glue, whatever you fancy. Should be able to patch it back up with the missing piece(s) if you still have them. It would take some time and patience, but well worth it. If you DONT have the missing parts however, all I can think to do is find some sort of water proof material, stick it over the hole and tape it or glue it there. You could try taking it to a shop and see if they do repairs, but you'd need to leave your slide at home and clean it out thoroughly.