fungus will grow if you don't clean out your instrument

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A saxophone player will discover that their G# key will stick after about 3 months.  Swab out your sax every time you play.

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A trombone player discovered that his instrument was a whole step flat after 3 years.  Empty your condensation key every time AND give your trombone a bath in tepid water about once a month or once every 3 months at least.