Hello, I'm trying to remove and replace this valve (in picture) but cannot unscrew it. Have tried adjustable wrench and plumber wrench plus WD40 to loosen but it doesn't budge. I tried quite a lot of force -but I can feel the whole unit moving and threatening to come away from the wall if apply too much pressure. Does anyone have any suggestions? I thought a spline or twelve-point fitting on a ratchet wrench would provide a tight grip around that round fitting. I only have a small socket wrench set so will need to buy the right tool so want to buy the right on. Thank you
