The very nature of air tools has them "living" in environments with dust and grit. To keep dirt out of the leader hose on my air tools I cap them with baby bottle nipples on the quick disconnet fitting. They are a good fit. . If you know someone raising an infant the price and be really right as they need to be replaced, but they are still good for my purposes. After a while they do get brittle and they no longer work for my purposes, but I usually lose them before that.
Perhaps there is a reason this isn't a good idea. I would be please to hear you ideas. Robin