This is exactly what those cheap "throw away" cloth towels, in packages of 50-100 at SAMS & COSTCO, are for. I use a lithium complex grease, rated for salt water use (outdrives of boats, boat trailors), and wipe off (not real compulsively) both sides of the fitting - otherwise, the whole area is covered with dirt that I have to scrape off just to get at the grease fitting the next time service is due - so, you're going to wipe it off (at least the zerk side) sometime, might as well be when you put the grease in.