I have seen several online headshops that sells 'oil water pipes' which is a base pipe that has been modified to fit into a female bong peice. Also, if crack isn't soluble in water, you should be ok pulling a hit through it without having to worry about it dissolving.... however, theoretically, if the water cools it down enough, the crack would resolidify in the water... so it's probably best to pull a tiny test hit through to see if it works before you throw an entire 20 rock in there and watch it come out as particles in your bong water