Older Kenmore Dishwasher stopped draining

As above. Instead of being spottless and drained, when done cycles, there's now dirty water at the bottom. I've just ran 5 cycles. It does drain every other time, but that's 3 that don't work. What's the first thing to check?

Thanks in advance.

I've read the other posts on Kenmores. Blown through the drain hose. Took off the "pump cover?" from inside, can't find any kind of filter I can get to. Underneath, the white plastic extension seems to come right from the inlet to the hose with a little guard on it, but that seems to be it.

Model 665 or 110773811