I finally got around to the analysis. When I spliced a hose with a funnel onto the drain tube, I was able to pour water down the drain with no trouble. I hooked some flat discharge hose onto the check valve and expected to find that the pump did not work, but it did. The rate did not seem to match what I was warned about, but I decided to button it back up and give it a try. I was gratified to find that the DW cycled normally. I guess there might have been a clog somewhere that we inadvertently cleared.

Thanks