Enough procrastination. Today I installed the new black water tank valve and replaced the drain coupler. Not too bad of a job, not as bad as I thought it might go. We left the tank "empty" since we drained it last time in Pismo Beach and I tilted the RV away from the drain end to try to keep "stuff" inside the tank. I still ended up with a gallon or so of stuff that drained out into a tub. I'm glad that at least the drain valve seems to be a standard item so the replacement fit well.
The replacement drain coupler will be the last replacement possible without replacing most of the rest of the drain piping. For this reason, I added a protective skid on the bottom of the drain pipe to protect the drain coupler from damage as we bottom out on just about every speed bump and driveway entrance.
Above left is the black tank drain valve that was replaced (the dark black). Above right is the drain coupler that was replaced (again, the dark black.)
Above is the service compartment where the drain hoses are kept (top center and bottom left.) The drain outlet is on the bottom left. Note there is very little ground clearance.
A nice long shower and the experience is almost out of my mind now. As bad as I try to make this project sound, the worst day rv'ing beats the best day working everytime!