general recommendation is 50:50. Want the alcohol to assist in getting the water to get out and disinfect and the vinegar to protect the ear canal from drying out too much.
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50:50 per DAN
Not quite:
"Making Your Own
So what's all this leading up to? "Home brew" to prevent ear infection, as many of our members wrote in to share with us. White wine vinegar is 4-6 percent acetic acid, and if it's mixed with an equal amount of isopropyl alcohol, it would probably work fine. Using undiluted vinegar may make the solution too acidic and cause irritation. Using less alcohol may be wise if you find that the 50:50 mix provides too much drying - this can make your ear canal sore after several days of use.
In principle, just diluting the acetic acid 50:50 with water might work since it appears that the acidic pH is more important than the drying effect of the alcohol."