Apply this material with a toothbrush, cloth, or cloth. Do not use steel wool, sand paper, files, etc. because removing metal will cause leaks. Most common is the lanolin-based slide grease. It can be purchased from music stores and although it seems expensive, the small bottle will last a long time. Only one drop should be used on each slide.
Some people like to experiment with grease as well as oil.
Simpler variations include adding a drop of valve oil to slide grease. If it slides down quickly, you have a loose fitting slide and need to apply the proper amount of lubricant. Space Filler is the first step, then possibly moving to thicker oil or Anhydrous Lanolin. If it continues to slide down quickly after using thicker grease, you may have a leaky 3 rd valve. Some simple habits can help preserve the appearance of you horn.