Sounds like the seller knew there was still a problem, covered it up and failed to disclose it. House inspectors are rarely held accountable. The realtors will also probably be useless. Neither one of them will want to be dragged into court, spending their time and not getting paid for it. Doubtful you will get the seller to admit there was a problem or pay for the damage - all they have to say is "it was ok when we lived there, this must be new damage that happened after you moved in". Dealing with a lawyer and getting involved with a lawsuit is your best bet - but even that is not a guarantee, and it may take a long time to see any results. You may want to call your insurance company, pay your deductible, and see what they can do for you. But if you don't have flood insurance, you may not get any help from them either. It's supposedly a big no-no to fail to disclose things like this, but even after this does happen, it seems like nobody is held accountable anyway. I'm sorry to hear this is happening to you. I hope you get some good news soon.

FYI, for painting a tricky surface like vinyl wallcovering (or laminate cabinets & furniture) USE THE PROPER PRIMER!! Most paints/primers aren't formulated for sticking to vinyl, which is why some run into peeling problems. Your best bet is to use a primer that's designed to be a bonding primer, like Zinsser BIN or Zinsser Cover Stain. Both say they'll stick to all surfaces without sanding (though light sanding to scuff up hard-to-bond surfaces is always a good idea). Check the labels - most primers can't make that claim. Glidden Gripper primer or Sherwin Williams Adhesion primer are other good options. Kilz is a fine everyday primer, but it's not designed to be a super-adhesive bonding primer for tricky surfaces. Glad some of you have had luck using other primers, but for anyone just beginning this project, be careful and do a little research before you choose your supplies. Since you have a double-whammy of vinyl-hard-to-paint walls and smoke damage, I'd recommend Zinsser Cover Stain or another primer that can claim to stick to any surface while also sealing odors/stains.

Ditto Buehl. Just push the button down again and it shuts off. Push for "on". Push for "off". And the water pipe story is humorous. Well, maybe to someone who isn't you! Glad you didn't have years of damage.

Replaced four fixtures? Licensed plumber? A year ago? Well, I'm not there to look at it but from your description it seems to me too little/simple work to fish for error from experienced professional. Possible, of course, but not likely. I suspect other cause. Also too much time passed to expect any particular response. Your chances of demonstrating that he caused this damage are pretty small, I think. And if you've ever been near a court room, you'd know that thinking of making a case of this is pretty unrealistic. Much time and money will be expended to take your chance. Then, assuming you prevail, you'd still have to collect the judgement -- which is an entirely different thing. How to proceed? Move ahead on your own and get the job done. Leave your suspicion about the plumber unresolved. The time, expense, and inconvenience of making any particular case about that wouldn't be worth it. And, from what you've written, I doubt his work was faulty.