when I remove the packing nut would it help to use another wrench to hold the bottom nut.. or.. (where else?) to avoid stressing the piping
My washing machine valves had the same issue. I replaced mine without holding back with a second wrench. Everything for fine for a few months until blam, one night the solder joint at the bottom of one of those pipes let go and dumped a bunch of water into the crawlspace. I'm convinced that I weakened the joint, and created a ticking time bomb.
So yes, always avoid stressing the pipe. The damage you cause may show up later at the most inopportune time.
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