@pawster According to Medicare logic (not mine) any substance dispensed by a piece of durable medical equipment, covered under Part B Medicare, also falls under Part B, Medical, not under Part D , Prescription Medication.
Saline is covered, along with nebulized solutions. I don't have access to my previous messages right now, but there is a document that explains the codesmwhich must be used, then it is covered 80%. Look at the 7% saline discussion to find the link. It is all in how the doctor codes it. Because my supplement covers my 20%, when the pharmacy codes it correctly my copay is minimal.
The people at Medicare explained that it falls into the same class as saline used to flush IV PICC lines, and is classed as a supply for durable medical equipment.

If you ever helped draft Federal Regulations, as I did in my career, nothing would surprise you. The underlying rules, which have evolved over 100 years, are arcane and incomprehensible. Then the public gets to comment, and the lawyers get to emend. The end result is always a surprise to those who do the initial draft.
Sue