I've installed a new bathroom vanity. The drain line, which comes through the floor, not the wall, is in the exact center of the vanity; the drain from the sink is likewise centered. How do I install a trap given the two pipe are centered exactly above one another and are not offset? Do I even need a trap for that matter? (The drain ties-in to a shower line.) Thanks for any help or guidance you can provide.

"How do I install a trap given the two pipe are centered exactly above one another and are not offset?"

You get creative and offset the "S" trap. Depending on the size of your pipes get a couple of 45's, a slip to compression fitting and some pipe and build a off set at the base of the chrome "S" trap. When you're connected to the drain pipe then cut the trap back and connect the offset with the compression fitting. Sound like a plan? Regards, Tom