Use a good hole saw and keep the acrylic cool and most important let the hole saw do the work for you dont press too hard especially when you are almost all the way through the acrylic.
I would do ALOT of research into this, talk to people who have DONE IT, ask your LFS of local Plastic Company about how to acheive this, and if there is a special drill bit which is recommended (this is actually the case with GLASS) DON'T BE AFRAID TO BUY IT, or have a professional shop do this drilling for you... The last thing you want is to destroy a expensive tank because you tried to avoid buying a $50 special bit or something...
You do not need a special drill bit, just a good quality hole saw. Keeping it cool will make the edges of the hole smoother. Go slow and let the hole saw do the work. I have drilled my acrylic 150 tank and numerous acrylic sumps and never had any problems. If you go at it like a mad man and push like hell on the drill you may crack it. Good luck!
This tank has the overflow in the middle of the tank. It's about 8"x4". But it's not drilled. The previous owner had about 6 rios crammed into pumping water to various filters and what not. I'd like to simplify it to one sump.
Let jst say that I have 4 drains drilled and they are 2 - 1" drains and 2- 3/4" drains and thats just enough drainage for my 180g. I have an amp master 3000 pump. How much water do you want to flow thru your sump? I suggest you drill more than one hole. It sounds like you have enough room in your overflow to drill more than one. You may want to add another overflow if you are going to drill it. You can only handle so much water with that size overflow.
I don't know if you care, but a super cheap 2" bulkhead is a toilet flush valve from a hardware store for $7. Only one side can be mated to standard PVC thread fittings, but the side inside the tank doesn't need PVC connections anyway. HTH, Matt
Glenn, buy the plumbing parts first so you know how big the hole you can make to comfortably accomodate 2 drains. You can make 2 bigger one's (1" or 1 1/2") for the drain and 2 smaller one's (3/4") for the return.
Here are a bunch of bulkheads and the hold sizes. For your size tank I would go with atleast 2x 1.5" or 2x 1". I found that my 2x 1" on my 190 can suck about 1600+ gph with two 1 1/4 durso standpipe. But to be safe I would go with 1.5" bulkheads.
Also drilling acrylic is easy. Just go really really SLOW. Make sure your hole saw is new and sharp. Stop every now and then and let the acrylic cool down while drilling the holes.