Determine the type of fitting
The first and the most important step is to determine whether the fitting is made up of solid brass or is just a metal coated with a brass layer (a very common occurrence made possible by the process of electrolysis among other techniques). The cleaning methods in the two cases will be totally different. In case the fitting is of solid brass, mild acids can be used on the surface of the fitting, but that cannot be a option in case of brass layered fitting.
The best way to distinguish between the two types is by using a magnet. It is often the case that brass coating is done on object, which has been made of low cost iron, which will immediately attract the magnet. If however, the base metal is non magnetic, then take a knife and scratch the upper surface of the fitting at a place which is not visible. If the surface beneath the scratch is yellow, the base metal is brass.
Remove Dirt and Debris
After determining the base metal, clean the surface of the fitting with the help of a velvet cloth or soft brush in case some surfaces are hard to access.
Wash with Soap Solution
Now prepare a soap solution in lukewarm water, apply it over the brass surface with the help of a soft cloth and then dry it immediately.
Wipe off with lemon juice or vinegar
Make a solution of lemon juice or vinegar in water in a ratio of 1 to 9, and softly apply it on the surface of the metal to remove discolouration and tough spots. Immediately remove the mixture from the surface with the help of a wet cloth. This process should not be done more than twice in a year.
Polish the surface
You can now polish the surface.