You're right, it's not the same. I'm sorry in the bottle it is precisely measured, into distilled water, and sterile packed. But it is still water and sodium tetraborate.
What you can try, I'm not a vet. 1/4 teaspoon of borax, in one half pint of warm tap water. Stir the heck out of it and leave set for 10 minutes. Either poor it off slowly leaving into another jar, leaving what didn't dissolve behind, or just poor through a coffee filter. Use a bare (needle...