Frankly, when I was a kid I used vinegar as a stop bath. What's the difference in food grade acetic acid in a bottle of vinegar and photo grade acetic acid from a chemical supply house? None that the film knows about.
The local druggist gave me the 1+3 proportion when I was trying to buy photo chemicals. In the tiny town I grew up in the drug store was where you bought any kind of chemicals except farm chemicals.