Its advisable that you contact your LFS
to see if they can do it or if you have a glass shop around contact them and ask what they would charge to drill the hole for you. For best results you must use a diamond tipped hole saw and to keep the glass cool you must have water flowing over the area being cut to remove the glass and keep the entire thing cool.
Now that I have the stock reply out. If there are rounded corners your tank is most likly acrylic. This is a form of plastic and the same rules apply as far as keeping the cut cool by using water. Since you can most likly use a dremel to do the cutting but you need to keep the entire area cool by wet cutting its not advisable to use an electronic cutting device. Again I would contact the local LFS
or glass shop. A hole should just be a few $.
Establish the size bulkhead you want. IE you may want to use 1/2" pvc
. If this is the case look for dimensions on 1/2" bulkheads and it will tell you what size hole to have cut. Most likly 5/8" or 3/4" for a 1/2" bulkhead
has a wide assortment of bulkheads and other tank fittings.