I'm setting up a used 120 g tank with a single corner overflow. The overflow has two drilled holes (1" and 3/4"), I'm converting it to a herbie style drain and running an over the top return. My question is, will the 3/4" drain and 1" emergency drain be enough flow for the 120 gallon tank? I also have a 40 gallon sump and have not purchased a return pump yet.