Remove four screws to get the two access covers off the lower front. Set your drain pan in place, and back off the big spring-type hose clamp from the rubber elbow you'll see at the end of the check valve. Slip the rubber elbow off the end of the check valve and you'll likely have this.
Patience is needed here. It took four half-fillings of that big frying pan to completely drain the dishwasher.
With the draining over with and everything cleared away, it's fairly easy to unscrew the check valve to examine it. Here's a view of the check valve out of the appliance.
That thing's inside diameter is only 10mm, so it doesn't take much to clog it. Here's what I yanked out of it with a spring hook.
I have no idea what that grotesque little object is -- it's quite hard, and it's certainly not something that we eat around here. Whatever it is, it had no business getting into the dishwasher. This is why the very first thing the user's manual tells you is, "Scrape large food soil and hard items (toothpicks or bones) from dishes."
Anyway, with the check valve and its gasket-seating surfaces cleaned, everything went back together easily. Before replacing the access panels, I ran a 'fill' and 'drain' cycle to check for leakage. All was well, so the dishwasher is good to go again.
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Note:
[1] As I understand it, the drain check valve is there so that in the event of some freakish mishap with a sewage system (as might occur in a flood, say) sewage water can't back up into the appliance. That's an excellent reason for the check valve to exist, but it does make for a somewhat constricted drainage opening.
The actual 'valve' inside the part pictured above is just a resilient flapper-valve located at the point where the diameter increases. I tried blowing through the valve in the 'check' direction, and it leaked, so how much good the valve would do if it were ever actually needed is questionable.
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