A three to one (or 2-1) mix of water and common distilled (unflavored) vinegar is the usual solution for washing the melodica, Hans. It eliminates odors as well as cleaning. Search here for “melodica bath” for more details. I normally soak the melodica for an hour or two in the solution, then blow it out several times, working the release button and all the keys. Then rinse very well and blow water through it a couple of times and dry out. Try it on the Yamaha first. This can be done without taking it apart, though I sometimes do take it apart to see whether further cleaning is advisable. But be careful not to bend the reeds or their gapping (space between the reed and the reed plate). I have not done this with button models, but it’s pretty safe with any model that does not contain wood (in which case I wouldn’t soak it). I also wouldn’t do it on a very old melodica with fragile deteriorating pads and such, for example old Italian models.