anyone have any experience cleaning or rebuilding the old EW petcocks? i took them off today and they're pretty nasty, didn't want to just throw them into carb cleaner because they look plastic/nylon-ish. anyone have advice on what to use to clean them, tools, chemicals, etc. also is there a way to take the screen off to clean things? it's so cruddy i can't tell and i don't want to just start yanking or twisting on it not knowing any better