Disassembled internal dishwater assembly looking for any foreign debris that might be clogging the dishwasher drain system since zero water was draining out. Nothing found. The Check valve assembly was the next logical problem. Replaced Check Valve Assembly. Put 1 gallon of water in dishwater for initial drain/leak test and hit drain button. Unit drained all water out of dishwater like normal. No leaks around valve assembly. Have not yet performed a full wash cycle for final confirmation that everything is normal. Replacing the Check valve was a 30-minute job. Checking for clogs inside the machine took about an hour.
The internal 1 way rubber valve in the old assembly had failed after 18+ years.