I have not cut any holes in my tank or sump yet. My returns were going to be two 1/2" bulkheads, one each running the IM Spin Stream. Originally I was going to run a 1" overflow from the tank to the sump. I started thinking that one 1" drain line might not be enough so I could run a 1.5" Durso standpipe, through a 1.5" bulkhead and bush down to 1" at the sump bulkhead. I became concerned because I figured it would not be a siphon and maybe 1" would not be enough. If 1" seems adequate than I'm all for sticking with 1" because I already have all the bulkheads.