stupid question on location of drilled holes in aquarium

[dkhester16]

going to buy a 180 gallon aquarium , and the usual position I see are the back corners for the sump inlet and return holes . what keeps the water from looping from the return back to the inlet if the holes are drilled behind over flows?
also I would like to say hi to all the fellow fish lovers , as this is my first posting / question Doug hester

 

[CAPSLOCK]

You want to have the return line come back up through the overflow and out into the tank - the line will head out into the tank at least a few inches. Some of the overflows even come with a little pop out that allows the return line go right through with no tools required. Some people opt to go over the top of the overflow.

Alternatively, you can drill a totally separate return line anywhere, if you are comfortable drilling through the back glass (it isn't as difficult as it sounds). This way you can use the normal return line hole as an emergency drain instead.

Google "durso standpipe" for a good way to easily make the overflow much quieter. Basically it's a pipe that raises the level of the water in the overflow so it isn't splashing down the whole way and making a ton of noise doing so.