Well we park for months at a time and can leave the grey tank open all of the time and not worry, so you really are talking about a way to leave the black tank open, correct? $200 - for that I can walk out and pull the lever once every two weeks (we have 80 gallon black tank) - since we are about the place anyway, a simple pull doesn't seem that hard. In fact, after 8 years on the road, I'm still trying to figure out why everyone has so much trouble with their tanks. We seldom look at the gauges - 10-12 days for the black tank, about 6 days for the grey when using the w/d and often just leave the grey open until the day before I dump the black tank.
Barb