Something that may help a little in the meantime is bumping up the humidity a little.
My vet suggested this as it helps to keep the mucus thinner and easier to clear.
I am having serious doubts about this vet. I do however remember reading here recently that someone thought their snake had an RI, and it was really stomatitis, which is an infection of the mouth, throat or lining of the digestive tract.
I don't think swimming is going to help your snake one little bit. I do think you should do your best to find another vet, which is probably not going to be easy. I think your vet should at least attempt a culture of this mucus. When I had to deal with an RI, my vet didn't even consider Baytril, she said it's not very effective anymore. If I remember correctly, I think Dr Stahl does phone consultations, so that might be worth a shot.
I wish you and your snake all the best.
Gale