A key to good horn playing is a well maintained horn.  If your valves are slow or sticky, then you won't be able to play up to your potential.  If slides don't move, you can't make quick tuning adjustments during a performance.

 
Overall Maintenance

  1. Never eat food or drink any type of sugary liquid, such as soda, juice, or even sports drinks right before playing.  If you do eat or drink something, make sure that you brush your teeth.  This will remove anything left over in your mouth.  If you follow this guideline, you will encounter fewer problems with your horn.
  2.  Clean your horn regularly.  This will save you money in the long run, because you won't have to get your horn chemically cleaned but every several years.

Maintaining Valves

  1. You should oil your valves with some sort of valve oil or rotor oil once a week.  If you are unsure of what brand to buy, Al Cass is always a good choice.  You can never use too much oil.  There is such a thing as wasting oil, but never using too much.
  2. You should oil under the valve caps and oil the bearing next to the valve stops with a thicker oil.  Key oil works well.  I have also been told that sewing machine also works well.
  3. Oil the valve springs to prevent them from becoming sticky and slow with valve  oil.
  4. At least once a month, run some warm, soapy water through the valves.  Try to use either the garden hose or put the horn directly under the tap.  Nothing is really going to be removed by simply pouring water into the valve slides.  After rinsing out the valves with clean water, be sure to re-oil the valves.  Doing this once a month, helps prevent lime deposits from forming in the horn.

     
    Maintaining the Tubing

  1. Plain and simple, wash out the tubing with plenty of warm, soapy water at least once a month.  As with the valves, try to use the garden hose or put the horn directly under the tap.  This will help remove the grime.  
  2. After doing so, re-rinse making sure all the soap has been rinsed out.  Otherwise, a soapy residue could be left inside.

    You should, ideally, have your horn chemically cleaned once a year.  This is especially so if you tend to play your horn after eating or drinking anything sugary.  However, if you brush your teeth before you play, and you maintain your horn well, you may not need to chemically clean horn more than once every few years.
     

    Maintaining the Slides

  1. Wipe your valves clean with a rag.
  2. Grease the valves with some sort of lubricant.  Any standard slide grease will work.  I like to use the slide grease that comes in a Chapstick-type container. I feel that it is easier to apply.  (I'm not saying use Chapstick!)
  3. From time to time, it may be necessary to really clean the slides.  For that purpose, Brasso works well.  I have also been told that carburetor cleaner works really well.  However, these are chemicals, and they can remove some of the brass off of the slides.  I would not suggest using any harsh chemical like mentioned above on your horn very often.  If you are unsure at all, do not use them!  If your slides are really dirty, I would suggest getting your horn chemically cleaned by a professional.

If you would like some additional information, Eldon Matlick of the University of Oklahoma has written a terrific article!

Also, Johnny Paul of Johnny Paul's Music Shop wrote a great article on the subject.