My 300G has a overflow box similar to the drawings shown here except in a traingular shape with 2 x 2" bulkheads ... 2 x 90 elbows ... flex tubing to the sump ( no durso ) ... ( 4MDQXSC as a return pump ... about 1000 G / Hr going through the sump ) ... al this behind a wall in basement so on show side no noise
This design gives you the most tank space IMO while skimming the surface of the water quite effectively
Cheers