: Craig, The first thing NOT to do is do not plug that drain pipe to prevent leaking. That is your relief valve exhaust. The pressure and/or temperature inside your water heater is probably excessive and causing the relief valve to leak. You need to have a professional find out why. You may have closed the system recently by having a dual check valve installed by your meter. Now you will have to add an expansion tank to absorb the thermo-expansion caused by the heater. Another possibilty is a bad gas valve causing the water to become too hot. Either way its time to call you friendly neighborhood professional plumber.