Anchor box not draining... HELP PLEASE?

[MasterBaiter]

I would try some air. Start with a lower pressure and work your way up. I'm guessing the line cannot be accessed so cracking it with 100psi would be a bad thing. You may just have a kink in it that some muck has clogged it. Where does it drain to? Maybe you could unclamp one of the ends and twist it, maybe whatever is causing the kink will hit a different spot on the hose.