drain line

So I have an custom aquariums over flow box drilled for 1.5 pipe 2400gph. Didn't realize till now all the plumbing supplies I purchased are 1.25 would this be OK to reduce from 1.5 to 1.25? Loss of flow rate? I'm running a bean animal with the 1200 reefmat

Hi Friends, plumbing my first tank and have a question. The overflow box drains have male threads to secure the drains into the box, so is best practice to use, for example, a female x slip union then the drain pipe (thus utilizing the threads that remain protruding after the nut) or simply...