Back drilled tanks

[George]

How many holes are there in the back? For 2 holes, you can do a herbie. For 3 holes, you can do a beananimal. Return can be over the top or use one of the holes (if latter, one less hole for drainage). You should build an overflow for sure so that there won't be much water draining to your sump in case the return pump stops for whatever reason.
You can check out my build thread for a herbie and a coast to coast overflow.