if you drill at the bottom of the side, then you'll need an overflow box that extends down to the bottom of the tank. This will conceal the plumbing inside the tank, keep the surface of the water clean, and keep livestock out of the drain. to help quiet it down you'll want a durso standpipe in the box. without knowing what your pump will be its hard to say what size/how many drains you will need. One large drain ( say 2" ) will handle a lot of flow but will make bulky plumbing. smaller drains will have smaller plumbing but you will need multiple drains and you don't have a lot of room on the narrow side of the tank for drains. if you want to maximize flow and minimize noise, then you'll want a siphon system. to do this safely you'll need 3 drains. i used this method when setting up my 135 and it works extremely well.
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