Hi. I'd like to know how to convert a double sink and vanity to a single. The sinks are independent of each other. I want to install a single sink vanity. How do I cap off one connection?

Take the drain trap assembly out of the compression fitting at the back of the cabinet (or floor if you have an S-trap). Remove the bonnet nut, go to the hardware store and get a cap that will fit those threads (usually 1-1/2" ips), thread it on after wrapping the male threads with 3 or 4 layers of teflon pipe thread tape.

Now if you have a rigged system where both sinks go into one drain fitting, then you just have to get the parts to eliminate the tee (for the second sink) in the drain tubing.