Mine is 1-1/2" off the back wall OD (1-1/4" ID) x 4" tall and 30" wide. I wanted to keep the overflow 9" off the side glass, hence the 30" length. My external box is also 16" wide, 4" deep but I made it 16" tall to give me room for the drain lines. I wish I had taken some better pictures of it before I placed the tank so I could share them with you. I have three 1" drains, a primary full siphon, a secondary drain that gets just a trickle of water and a third emergency drain that is 1/2" above the secondary that should never see water but lets me sleep at night! I use a gate valve at the bottom of the primary drain, the other two drains do not have valves.