draining pressure relief valve

I just installed a new well tank and decided to install a pressure relief valve. The old tank/Tee did not have one. From reading some posts here I noticed that people have ended up with flooded basements when excessive pressure opens the valve. I want to plumb a drain to outside using pvc in the event that the relief valve would open. Thus preventing a big mess in the basement.

Is this acceptable or common practice?

Very much acceptable and is the best thing to do. A lot of people don't, then wish they had.