Well, we haven't had a problem with the graywater tank, but the blackwater one was special. Slow to drain, easily clogged, the works, for 9 years.
Last September, the valve refused to close. Not good with a blackwater tank. A flashlight revealed a large disk of polyethylene blocking the valve. And the only way to get it out was to grab it by hand. Ugh.
Where did the disk come from? I assume it was the cutout when the drain was installed into the tank.
Now the clincher. Friends who had owned two trailers from other manufacturers had exactly the same thing with both of those trailers