The port with the larger diameter, located towards the body to the lower left if the box is mounted in the vehicle. the smaller port located outwards to the input shaft is the return port. at least that is how mine is.
is it nec. to have a high pressure hose for the return. My sag box has a low pressure (just normal hose) to a oil cooler then back to the pump. but the high pressure inlet does have a high pressure type hose and fitting.