The stopper in my bathroom sink does not come up. How do I fix it? --- Joan, Columbus, Ohio
On most sinks, what you have is a little knob somewhere on the faucet. You pull the knob up to close the stopper and push it down to open the stopper. What's happening behind the scenes is the knob is connecting through a strip of stiff metal down to a rod. The rod goes into a thing called the "pivot nut". Inside the drain pipe, the other end of the rod is pushing the stopper up and down. If you look under the sink, you can see the piece of metal, the rod and the pivot nut. It's all obvious.
So what could go wrong? Hopefully it's the strip of stiff metal, which has either broken or come loose. If it breaks, replace it (easy to find at the home improvement store). If it came loose, look at another sink to see how it attaches and then re-attach it.
The other possibilities are a loose pivot nut (tighten) or a broken rod (replace).
For more info, see the plumbing library.