Collect your brass instrument and supplies and dissemble them, including their slides, piston and valves. Set the pistons and valves aside.
Take a bathtub and fill in warm water. Make sure the water is not too hot, as the hot water can damage the lacquer on the instrument. Therefore, the water should be slightly warm. Now take a small amount of dish soap or detergent and mix it well in the water.
Use a cleaning snake or a toothbrush to wash the instrument thoroughly. Cleaning snake will be used to clean the inner parts of the tubes. You can also use a washcloth to clean the inner parts. On the other hand, toothbrush will help in cleaning the mouthpiece and some other small areas.
Take a shallow dish and fill it with soapy warm water. Now put the pistons and valves in it. Make sure they are covered by water completely.
Rinse the instrument and remove all the soapy water from it. Also, rinse the pistons and valves carefully. By using a towel, dry them all.
Take a valve casing brush and use it to clean the pistons and the valve casings on the instruments.
Make sure the brass instrument is completely before proceeding to the next steps. Take a small amount of slide oil and apply it to the slides that were set aside. Now take a large amount of oil and apply it to the valves. If you find any red spots, which are known as dezincification, put some extra oil. You should do the same if you find blue or green spots, which are indicators of corrosion.
Reassemble the instrument and it is ready to be used again.