I'm re-working a tile shower set on a concrete slab, and have removed all tile and mortar down to the slab, ready to start rebuilding. However, I can't get the middle section of the brass drain fitting off so I can put the new waterproof membrane under it. It's about 2-5/16" hex nut - I've been putting every penetrating oil I can find onto it, trying to grasp the edge of the nut with a pipe wrench, but can't bet it to budge.
Any suggestions? (I'm not at all interested in cracking the slab to replace the entire fitting!)