Ever since I started using Hypertonic Saline I’ve been mixing 3 mL of 10% with 2 mL of 3% to make 5 mL of 7%. (National Jewish recommended doing this years ago before the 7% solution was available and I’ve been doing this since.)
Both the 10% and the 3% Hypertonic Saline are available in 15 mL vials. Although the vials are marked “Single-use”, I use each 15 mL vial of 10% for 5 treatments and each vial of 3% for 7 treatments.
The vials have mL markings. I enhance the vial markings with a felt pen - every 3 mL for the 10% and 2 mL for the 3%. This makes it very easy to “squeeze” the correct amount of each solution directly into the nebulizer. (I have found it easier to mark several dozen vials at a time.)
The vials of Hypertonic Saline I am now using are made by MYLAN as “Sodium Chloride Inhalation Solution, USP”. They cost less than $1 - even without insurance. Since each vial is good for multiple treatments, the cost is fairly low.
While this may be slightly less convenient than using the prepared 7%, I have found very easy. For me, the occasional vial marking is the most inconvenient part of the whole process.
Note: When traveling, I do use the prepared 7% solution vials, since having the opened vials around for multiple doses could be a problem.
I hope this provides some useful information.