Quote Originally Posted by RockoC87
what is the right size hole to drill? i might want two overflows. Its a 100 gallon tank
It all depends on the brand of bulkhead you choose. Different brands use different size holes for their bulkheads. Best bet is to measure the bulkhead OR check out the website on where you are going to order the bulkhead. Usually they should list the hole required for that particular bulkhead.