Join Date: Jul 2010
Location: Outside Philadelphia, PA
Personally, I would not drill the tank for the returns. The slightest problem, and you will need to drain the tank to repair it. You get a leak, a bulkhead need resealing, a check valve needs to be replaced, and you have a major job on your hands.
With a return, yes , you can have similar issue if you don't use an overflow, but with an overflow, you can usually just drain the tank a little to make the repair.
I'm not a big fan of check valves. They always seem to fail when you need them. Over time you get some build up and other gunk, so if the water flow stops, they may not close. Then you got a flood.
I much prefer to run the return over the top rim, and drill siphon break holes just below the water line. Since there are no moving parts, they are much less likely to fail. Also the siphon break hole is a lot easier to clean. Just run a brush through them. A check valve needs to be taken apart to clean it. So if you drilled the tank, you either need to drain the tank, or install valves, so you can isolate the check valve and remove it for cleaning.
Granted, going over the top rim and down to where you want the flow doesn't look as pretty, but it's a lot less problems. Yea, I've done this both ways, and speak from experience.
BTW, you can get PVC pipe and fittings in gray or black, which goes a long way to hiding the returns and drains.
Another alternative would be to just have 1 or two returns an add some circulation pumps inside the tank. Much harder to hide those.