I suspect it has been sloshed, and the slosh is beginning to exfoliate. However, let me hit you with the symptoms, other than the trash coming out of the quick drain:
When the thing gets to about a quarter full, the engine quits. It has happened often enough that the owner takes great pains to not get in a situation where it could cause a forced landing. Happened to me on approach, about 700' agl, so I know it is real. It is the left tank, which theoretically fills the forward header? And it seems to happen either in level flight or in a glide - a clogged forward outlet? Anyway, I recommended an immediate removal and cleaning. Aircraft is fresh out of annual and extensive work - not by me.