I agree with Adam. However, from that point on, every time I washed the truck I'd be sure to spray water in there to keep it clean. Or even better would be to get a cover for it. One other thing you might try is WD-40. Spray inside and also on the tongue. Wait 3 or 4 minutes and then insert. That may take most of the gunk off.
Grab yourself a can of "Fluid Film" @ the parts store. Wire brush it out and spray liberally. Fluid Film is water resistant and does not evaporate. It is also a penetrating oil. Not solvent based, actually lanolin based. Good also on yours hands during cold dry weather to prevent skin cracking.
I would think that anything short of dry graphite will have some degree of dirt attraction. You would be better off with more frequent cleanings/re-sprays. I have found never-seize to coat things but spreads like crazy on everything it contacts. Class "A" mess to clean off your hands as well.
I'd just clean up the hitch with a grinder. Then lube the crap outta the reciever with whatever ya got.