I buy boric acid powder at the pharmacy and mix a small portion with boiled water. (You can find amounts online). You can soak gauze in it then apply it.
In the old days, and I mean in the 1920s-1950s - my grandmother always kept a warm pan of boric acid water on the back of the stove. It was that important to have on hand when raising six kids. They didn't have antibiotics for most of those years - so infections were drawn out with compresses and wounds were sterilized this way.