I put one in the gray tank as well. Getting grease off the tank walls is harder to do than get black stuff off the walls of the other tank.
That's why I've been using water softener in the grey tank. Helps Keep grease and stuff from sticking to the walls. The tank flush would be a great addition too. I think I may install one in my grey tank.
__________________ 2012 Coachmen Freedom Express 292BHDS 2009 Ford F250 Super Duty CC 6.8L 4.10
Husky Centreline WDH w/Sway Control
2013 Nights Booked: 38
2013 Nights Camped: 40