Returned and replaced customers water heater with new 50 gallon gas water heater. Installed a new pan and new thermal expansion tank. Reconnected to existing water and vent lines. Installed a new gas supply to the new heater. Customer had concerns about water that was dripping down a drain pipe when it rained heavily the previous day. Inspected the pipe and observed that it appears to be a vtr pipe. Customer stated the leak can’t be recreated by running any water and only seemed to appear during the rain. Recommended having a roofer inspect the boots for any roof penetrations for the plumbing.