The mixture I suggested would be pasty wouldn't it?! Gosh; I wonder where my mind is these days!
My dad was told 1/4 tsp soda to 1/8 teaspoon salt to 4 oz. of water.

Thanks for spotting the problem with the recipe Mark, sounds more like a solution for bee stings!
Lol!

I've borrowed the following info from this link, I hope it's ok to post it here.
http://www.nci.nih.gov/cancerinfo/pdq/supportivecare/oralcomplications/patient/

Cleansing agents can include "salt and soda" (1/2 tsp. salt and 2 Tbs. of sodium bicarbonate in 32 oz. of warm water), normal saline, sterile water, or sodium bicarbonate (1 tsp. in 8 oz of water). Hydrogen peroxide diluted in equal amounts of water or weak salt water can be used when crusting is present. (This should be used for 1 or 2 days only because it will keep mucositis from healing.)

A salt and baking soda solution neutralizes acids and dissolves thick saliva.