Snowman9000 - Please do show pictures, always easier to understand the description.
Teacher's Pet - I have also thought about an electric dump valve. Drain Master was the manufacturer and several years back I saw a sale on the $99 unit for $39 and I didn't snap it up. Wish I had as they are more expensive now
RV Upgrade for Drain Master.
Whenever you are in a campground with full hook-ups, it is recommended to leave the black tank valve closed until the tank is full and then snap the valve open. Our Model 211-S has the shower drain going into the black tank. It would not be nice to be taking your shower and the black tank gets full, having to dress, go outside to pull open the manual valve, and then finishing your shower. ;)