Soft wall?

Let me start off by saying that I have less handyman experience than my 2-year-old daughter. When it comes to home repair, I'm about as useless as a they come. So when I get the chance to hang a picture or a light fixture, I get pretty excited. Give me a chance to make some loud power tool noises and I'm in heaven. The problem is, I still haven't finished putting together my table saw. But I digress.
We live in a pretty big house for a family of three. When something goes wrong, it's easy to "move" into another area. The heat goes out? We can go upstairs for that unit. Toilet not stopping? Turn the water off and use another bathroom. A drain leaks upstairs for years into a wall and rots it from the inside out? Well, I may get to make some sweet power tool noise after all.

It all started with a towel rack hung innocently enough in my wife's downstairs bathroom. I almost never got a screw in the wall where I wanted it, so I had to choose a slightly off-center spot above the toilet. As I would later find out, the reason was because of a pvc drain. Who knew? Anyway, we've had a leak coming from the upstairs shower faucet for about a year. And a half. Or two. Whatever. We use our fair share of water. A few days ago, the towel rack fell from the wall. The screws came out and the wall was soft. I easily pulled the drywall back and exposed the pvc pipe where I could see water slowly draining down the outside of the pipe. Not good. From floor to ceiling, soft.
My wife comes home and I break it to her. "I've got good news and bad. The good news is that you get to pick any color you want for your new bathroom." She wasn't amused. I had to hide the fact that I'm actually excited about getting to rip my wall apart. Come on, when will I ever get to do this again? I can't mess it up any worse than it is now, and if I have to hire someone to fix my mistake, I'd have had to hire someone anyway. It's a lose-lose situation in which I'm the winner!
So here's the plan. I've got an actual plumber coming over this weekend, but only to stop the leak in the shower upstairs. That'll at least stop the water and buy me some time. (Titans in the playoffs? The house of falling cards has to wait.) Then I'm going tear the wall out and hopefully make my way to the joint on the pvc and seal the leak. If I can't see it from the open wall, supposedly I'm going to have to cut into the ceiling or from the floor above to find it. THAT'S the reason for this blog. (I know you were wondering.) I'm so bad with tools and construction and plumbing and putting things together with simple directions accompanied with photos that this will surely be used as a how-to n't for generations to come. Countdown to destruction: 3 days. Until then, I'm going to use a different shower.