I was never told to pump or not pump.
Seems like pumping could bring some old liquid back into the tube, but since the end is open anyway, it shouldn't make that much difference in chance of infection (?)
If the draining were slowing down, for whatever reason, seems like an occasional "pump" (almost sounds obscene, sorry) might get things moving along. I just pump mine to make sure it still works. If it were to get too tight I would think there was something obstructing.
Interesting to hear about. "to pump or not to pump, that is the question" LOL