[intarsiabox]

If you are planning on using Loc-line for the return line for current direction in your tank they only make it up to 3/4". You can use a 1 1/2" bulkhead if you want to (that is plenty big) as only the rate of flow that is being pumped into your tank will be flowing back down to your sump. I would put a valve on the discharge of your return pump as it will be putting out about twice as much flow as you need and you can tune it to prevent sending micro-bubbles into your display tank. Remember to build a putty dam around the holes you are going to drill so you can keep it filled with water to keep the bit cool and don't force the drill too much.