We used a solution of 2 parts white vinegar and one part hydrogen peroxide. This is to remove surface lead from the brass (based on this: http://www.howtobrew.com/appendices/appendixB.html). Not sure if it really matters as many feel the amount of lead in these fittings (meant for potable water) contain very little lead and the odds of any transfering into the beer is minimal.
Los Angeles Brewers 