Kenmore dishwasher won't drain: 665.13422k701

After googling, and particularly after reading this post I decided to take a look at the pump. Here's what I did:

1. Turned off power at the breaker.
2. Removed the bottom access panel (two screws).
3. Undid the drain hose.
4. Dried the floor (you can stop laughing now).
5. Turned power on at the breaker.
6. Pressed the "cancel/drain" button and observed vigorous action from the pump.
7. Pressed the button again to make it stop.
8. Turned power off again at the breaker.
9. Re-attached drain hose.
10. Noticed troubleshooting documentation in plastic sleeve, attached to interior surface of the access panel mentioned in step [2]; it makes me think the check valve is bad.
11. Replaced access panel.
12. Turned power back on at the breaker.
13. Verified that it still doesn't drain.

Replacing the check valve in the drain-hose loop will probably require pulling the dishwasher out.

The good news is that this machine is still under (extended) warranty. The guy will come next Tuesday. Fortunately, we still know how to wash dishes by hand.