Cleaning inside the horn
Cleaning the leadpipe is an effective way to keep the inside of your horn clean. The best way to do this is to use a cleaning snake.
To use a cleaning snake, remove the mouthpiece and the main tuning slide. Push one end of the snake into the tuning slide end of the leadpipe and carefully feed it through until it comes out of the mouthpiece end (from the larger to the smaller diameter). Then, gently pull from the leadpipe end until the whole snake has come through the leadpipe. Rinse the snake and repeat until it comes through clean. If the leadpipe has not been cleaned for some time, beware the sludge! This is an indication to clean the leadpipe more regularly.
It shouldn’t be necessary to wash out the rest of a horn which has been properly cared for, but if a horn has been neglected over a long period then washing it through with warm water and mild dish soap should be followed immediately by thorough draining and a complete re-lubrication to avoid the formation of corrosion in the valves. Likewise, a horn being placed in storage for any period should have the valves well-oiled and operated regularly to ensure they do not become seized.
It is generally recommended to ultra-sonically clean a horn once every year. Most shops will also check for any unsoldered braces, holes, or dents at this time. Usually, new rotor strings and bumpers are included in an ultrasonic cleaning.
Cleaning the outside of the horn
If your horn is lacquered then all that is necessary is to wipe it clean with a soft cloth. Over the years, the lacquer will deteriorate where the hands are most often placed. This is largely because of perspiration, so wiping the instrument after playing will help maintain the lacquer in good condition for a longer period. If the horn is not lacquered then it will normally have a dull appearance. It is quite safe to polish an unlacquered horn with normal brass polish but, since this has an abrasive action it is wise not to do this too often.