You can drill the closed loop in wherever you want, including the bottom.
I have seen some pictures of tank with it done through the bottom, with about 4 returns throught the bottom in different locations, then covered them with piles of rock to hide everything, so all you could see was a nozzle if you looked closely.
It depends on where your pump will be too.
Lots have the drain (into the pump) in the middle bottom of the back glass, then a t-d off return to the sides of the tank. Or you can run a manifold (PVC rimming the tank with multiple t's and nozzles) Some t of the returns twice so there are 4, returns to distribute water flow better.
My manifold has 7 nozzles of 1/2" loc line running off a 1" manifold. But my tank is not drilled for a closed loop, so my intake is a 1.5" pipe capped with many holes in it.
Hopefully that gives you some ideas, we would need to know more (where is the pump, is this in a fish room our out in the open, etc.) to give more specific advise.
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