What I mean is to plug the hole from which you disconnect the return line. The return line will be the one that has a screw clamp on the hose. The other line is the high pressure line which should be undisturbed.

You can either loosen the screw clamp and pull the hose off of the steel tube, or what I think is easier is to loosen the fitting and put the whole thing in the drain pan. You can then put enough tape around a bolt to plug the hole from which you disconnected the line.

It will be a little cleaner if you suck as much oil as you can from the reservoir before disconnecting the return line. Then you will only have a little oil dribbling down the side of the pump into the drain pan.

Don't get any bright ideas to use solvent. You could easily damage the pump or a seal.

Good luck,