Next time you see a water heater look for a little yellow tag that should be hanging on what is called the TP relief valve on the side of the water heater. This yellow hang tag tells about this valve and how it should be tested and installed on the tank. It is one of the most important safety features on a water heater. Properly installed and maintained this valve will help to keep you safe if your water heater decides to go haywire.
The following PDF is one of those little yellow tags along with a good deal of information about the valve, it was produced by a company that makes a device to help prevent improper connections of the required drain line to the valve .
Scott Patterson has been a professional home inspector since 1995 and works out of the Greater Nashville TN area. You can contact him at his office 615-302-1113 or on his cell at 615-870-4162 via text or voice.