My bath tub has a plunger type drain that seems to be stuck in the up position. I noticed this happening in a different bath tube and removed the plunger. I then used steel wool and cleaned it up. With this tub I can't get the plunger "un-stuck" to be able to remove it. I would imagine it is corroded and stuck in the pipe. What can I do to get the plunger free so I can remove it? I've tried WD-40 but that didn't work. Help.