When I first started using Hypertonic Saline in 2005, I use to “mix” it. (I’m not sure if they had 7% at the time.)
My doctor prescribed 10 ml vials of both 3% and 10% saline. I would mix 2 ml of the 3% with 3 ml of the 10% to get 5 ml of approximately 7%.
The 3% vials provided 3 doses and the 7% 2. It was extremely inexpensive!