So I was dumping my black water tank this morning. Everything was fine until I tried to close the valve. It was stuck solid in the open position. Would not budge a bit. I tried spraying a little WD...
I've never had a dump valve stick but the external valve others recommended is a good idea. Camping World (as well as some other RV parts suppliers) stock them.
Maybe mine haven't stuck because I add a valve lubricant to the black tank occasionally. The latest concoction was coconut oil based and it appears to work well.