Unfortunately those expansion tanks only come with a 1 year warranty, and for a good reason. If you have a pressure regualtor on your supply line, then expansion tank is an absolute must have. Drip is most likely caused by shutting off a faucet too quickly. Same for inlet valve on dish washer and washing machine, both of which close almost instantly. Most houses have "water hammer chambers" at faucets. These are just capped off pieces of pipe which ORIGINALLY contained air, which over a period of time is absorbed in the water. Turn off gas to WH first, then turn off supply line to house. Open all faucets, including outside ones, and let water drain. This is also a good time to drain sediment from WH. After all water has drained, close all valves, then go washing machine box, and disconnect cold water hose. Open cold valve, and blow compressed air into cold valve (no more than 75 pounds of pressure.) Close valve and allow air to stand in pipes and WH tank for about three minutes. Open valves to relive pressure, then turn water supply back on allowing water to run for a couple seconds at each faucet. Remember that the water heater will have to refill. Then light WH. This should recharge air hammer tubes.