Do a "reverse flush" where water is introduced into the bottom hose nipple and flows out the top. If you have an air hose handy, it's possible to rig a T fitting in the inlet hose and goose a quick shot of air into the flow to shock debris loose, but be aware that might also cause a leak to open up on a rotten radiator core.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!