Well, it does actually still stink, we have bathed it again, and bathing it seems to help for a day or two, then it goes back to being quite foul
Chris is also having problems with condensation building up in the mouthpiece - every four notes or so, he stops and wipes it out with a tissue because he says the smell from it is unbearable. I've tried getting him to keep the whole thing angled downwards so that everything dribbles to the end of the slide where he can blow it out of the little hole, but we're still finding the mouthpiece is filling up very quickly.
He has only had one lesson (30 min group lesson with a load of cornet players

) and then his teacher has been off sick ever since, so although he's doing quite well on his own (with a bit of help from me and the tutor book) I am worried that he will quickly get disillusioned by the smell / condensation problems and lose interest before he's really given it a proper go.
Any suggestions? I am wondering whether it really is because this trombone is so old, it's never going to be a pleasant experience. That would be a shame because it actually sounds lovely. We might look at renting one, but I wasn't sure if we would just encounter the same problems with a newer one, or if it's something that only happens to old neglected trombones......