Replacing 3/8 Faucet and Toilet stops on nipples

I am working on a bath remodel and replaced two of my shutoff valves and respective chrome plated brass nipples to my sink. I used BrassCraft 1/4 turn valves, but subsequently read that these valves (from HD) have a reputation for failing on occasion.

I was able to get a few Dahl supplies, and will be replacing the valves on those new nipples, as well as an entirely new nipple/valve on my toilet supply.

My concern is removing the valves from the nipples for the vanity supply. What do you find is the best method to remove a valve from a nipple without turning the nipple from the female adapter in the wall? How should I clean up the threads from the teflon sealant I used before installing the new valves?

Sorry for so many questions, but really don't want to flood the entire living area of my slab home. Sometimes get too OCD about this stuff...

I would appreciate any advice. Thanks!

If the nipple comes loose, and your fitting in the wall is anchored properly, I'd probably just unscrew the nipple, reapply pipe dope (you may not need to clean any existing off if it isn't chunky), and then reinsert. Note the angle of the nipple as you remove it to make it easier to reinsert and get the threads started without cross-threading it. You probably don't have enough nipple sticking out to put a wrench or pliers on, but that would work, too.

One of the first things drummed into are heads in trade school was always use two wrenches.

John