I dump in odin's salmon stream....
there are state and local regs that differ from place to place to place.
you have to check your's to know what's legal in your area.
I'm reasonably sure though, the storm sewer is a big NO-NO regardless where you live.
Most places allow dumping in a sanitary sewer.
when we're in town, we dump at the car wash.
..L.T.A.