Just cleaned up mine for my move down and worked great....I wouldnt even mix the vingar with water....just straight up vinegar will be fine.....I let mine soak in the bath overnight, next day it was new looking. you can also let the whole skimmer run in vinegar if you buy enough to fill up a tank to sit the skimmer in.
If it's really, really dirty; especially the pump, you can use muratic acid/ water mix (i believe it's one part acid to three parts water....rinse real well before putting back in the tank and your set.
This solution really works wonders on pumps.