Has anyone here ever done it? I have a pre-drilled tank with 1" holes for drains in the overflow and I want to increase the size to 1.5" or 2". Suggestions please. This is a tank that is currently housing fish.
I've done it, even with fish, but you do have to be careful. I'd get some scrap and practice on it first. You use a hole saw. You'll need to clamp some wood over the hole to give the starter bit something to drilll into. Once you get through the wood and the hole saw starts to cut a groove in the acrylic, you can remove the wood. Get a spray bottle and keep spraying the bit and acrylic by backiing it off every 10 seconds or so. You may also have to clean some acrylic off of the hole saw. Go slow and use a good variable speed drill. If you start it too fast and the hole saw isn't seated exactly right, you could crack the tank. I usually start the hole on one side and then finish from the other, but may not be possible for you. Be aware, then, that when you come through, it may chip. Not a huge deal with bulkhead fittings if the chips are small. Here are some pics. Patience is the key to success with this. Go slow, back it off frequently, keep the hole saw clean, and keep spraying the water. Acrylic is fairly soft and the hole saw will get through it quickly, but can also damage it pretty quickly as well.
Another thought while thinking this through, if you can clamp some wood to the inside of the tank over the hole, that allows for the starter bit and also will help to avoid chipping when the saw comes through the inside. Wrap a soft cloth around the ends of some wood that is inserted between the wood that's over the hole and the front of the tank. Use a very soft cloth and be careful not to scratch the acrylic. I did something similar when I glued my overflows in place. Here's a pic.
DO NOT skip on spraying the bit/acrylic with water either. It seriously sucks when your bit binds up and fuses to the acrylic...
Thankfully, it occurred when I was drilling an overflow box and not an entire tank. Ended up using a blow torch to heat the drill bit as I ran the drill. Eventually it melted the acrylic enough to free the bit - and I still got a clean hole. But the situation really sucked.
Thanks for the feedback. This looks like 4th and ten...time to punt to the professionals. I am the least handy person on the planet. However, if I do pass the task onto my LFS tank guy I can watch him to make sure he follows your directions and not crack my tank. I would have no words explaining to my wife why we have a couple hundred galllons of water in our basement. I do believe I will move ahead with this project this spring.