I want to put a timer on my hose bib for my garden. It leaks out the top when I try to leave the water on. I seem to remember seeing packing in some older hose bibs, it was like heavy,waxed or grease impregnated string. This is not my house and I don't want to screw it up because the main will have to be shut off to fix this. Please advise how this packing can be replaced.

Thank you in advance.