I used a serrated knife with a very sharp point to make holes in my tub. -shrugs- It's a lot more work than a drill or soldering iron because you have to twist the knife around to dig it in and make the hole and then go to the other side to even out the hole and clean it up, but it works just fine. Though once you make about 50 (and counting) holes in the tub you get really good at it.