My old tank I literally threw a pump behind a rock and ran PVC along the overflow up and out to pump water to the UV mounted above the tank.
In the new tank, I reused the old overflow holes on the bottom glass and repurposed them as a closed loop for my UV sterilizer.
Intake and effluent are at the bottom of the tank. I thought it was a good way to use the existing holes instead of just covering them up.
Your a brave man. Plumbing out the bottom scares the crap out of me lol..
My tank has a pvc bottom. It had four holes machined for bulk heads. I actually had pvc plugs machined from pvc rod to fit them then glued them in with weldon 10.