black water holding tank valve opens but won't drain

My strategy is to use the park's restroom for the big jobs and only deal with it once! Wish I could convince the wife.

I do use a packet of laundry detergent with five gallons of water on my way to the RV park. I then drain as soon as I get there. It is amazing how much stuff comes out even after previously using the black tank rinse. I would be leery of using a whole bottle of dish detergent. I'd be afraid of brown suds discharging out of my roof vent.

On to a more appealing thread!