The best cleaning agent for your valves is LACQUER THINNER. (Not paint thinner, lacquer thinner).
Dip the valve into the thinnner but don't immerse the pad or you'll be truly sorry. Let it stay in there for a couple of minutes and then rince it like crazy. Oil it up and you're good to go.
BTW, lacquer thinner really stinks, so be prepared for the stench. And don't get it on the finish of your horn.