Drill hole and use pop rivet
The only way to clean-it-yourself is to drill an 1/8" hole along the outside diameter close to the weld joint so all of whatever kind of fluid you put into to clean it will drain completely out.
After you are satisfied that it is cleaned and completely drained, put a pop rivet in the hole to seal it--DO NOT use the kind that the head pops off. You may want to put just a little epoxy on the rivet for insurance.
Use something like mineral oil to flush with--pour it in the snout and shake it all around. Then, flush one last time after the mineral oil comes out clean and clear with ATF.