Welcome aboard Medusa Is the drain hose indeed disconnected from the drain? That would be a weird thing, since it (the drain hose) is connected underneath the box to the drain (a nylon thru-hull fitting from the factory) via two stainless hose clamps.Most likely, the hose is clogged with leaves, pine straw, fish remnants, plastic, etc. Go with pete's recommendation of a blaster garden hose. Failing that...run a plumber's snake through the drain and hose.