Whirlpool AWM 049 not draining?

Stops mid-cycle and won't drain. I've taken the pump off and tested it, and it spins fine, impeller spins fine when connected to the power and machine is set to "Drain". I know the feed hose to the pump from the drum is not blocked, as I can drain it manually OK, and I've already had it apart to check anyway. When I connect the pump back up and disconnect the waste hose from the back of the machine it won't expel any water I pour into the drum from the spigot at the top rear of the machine (where the waste hose connects). How can I test that the pump is actually pumping the water OK (I can't just disconnect the internal waste hose, as it will simply drain the drum under gravity)? Any ideas? If I can remove the internal waste hose and confirm that it has no blockages, is it reasonable to assume that the pump is not working, despite appearances to the contrary?

Many thanks.