Back butter?

Two questions: 1.) Is it necessary to tape and bed the drywall (greenboard) before you install ceramic tile on top of it? 2.) Can the greenboard sit on top of the edge (on the very top of the ridge that curves up) of the tub or does it need to be hung just above it (no contact at all). Thanks!

well a job that i thought was only going to take an hour has turned into a project or so i think... hopefully with some help it won't be as bad... I have a shower that has dual faucets, the hot side valve seats needed to be replaced because the shower was dripping and no matter how hard you turned the handle it would still drip. The problem is this..... first I took off the handle. Then unscrewed the the next nut, almost looked like a compression fitting of some sort, could be wrong though. At this point shouldn't the valve stem pull right out? its loose but almost looks the the valve stem and body is all one piece? after the first nut was removed i even tried putting the handle back on and turn it loose and still nothing...... any suggestions?