I sometimes use a locking wrench to hold a pipe while I turn another compression valve. It keeps the pipe in place so I can apply torque to the other fitting. Background: This is image 21 of a repair project to fix a shower/tub diverter valve made by Barber Wilsons & Co Ltd. The handle which was supposed to divert water to the shower but it did not work; a plastic piece inside was broken. Unfortunately, since this valve could not be fixed from the front, it required a major operation to open up the back and replace pipes. I ended up replacing the defective valve with a Price Pfister valve-set so in future repairs will be easy.