Silencer for draining gas from diving tanks. Anyone who has ever had to drain residues of an old breathing mixture knows how hard it is to keep the hiss of the air at a bearable level even when draining the air relatively slowly. The silencer is attached to the tank valve and enables draining of the old air within minutes. Thanks to an efficient lowering of the sound level, the noise does not exceed the level at which it would make having a conversation anywhere near the tank impossible.