A dirty instrument negatively affects the response and well and the slide and valve action. Cleaning instruments with ultrasonics has the distinct advantage of penetrating complex geometry and removing tightly bonded contaminants from a variety of surfaces. When the metal breaks down from all the acids in saliva, salts, and scale build up in your instrument. The zinc is eaten away first leaving the copper behind. This is the reason it is called red rot because of the reddish spots of corrosion.
Most red rot happens in the leadpipe on most instrument.
The leadpipe tends to always collect the most amount of build up, so the consistent exposure to moisture speeds up the corrosion process. To prevent red rot from happening or to keep it from getting any worse, have your instrument professional cleaned to remove the scale build up in your instrument. Soap and water will not remove this kind of build up. Make sure to oil your valves and rotors, you really cannot over oil your instrument. It would be also a good idea to place a few drops of oil into the leadpipe after you oil your instrument as this well help to dissipate moisture and retard the corrosion inside.