Although the widely-used top-drain drum washing machines in the market are excellent in solving the problem of drainage drop, due to the limitation of the drainage mechanism, a small amount of stagnant water often remains inside the washing machine, which may lead to bacterial growth, dirt accumulation and moldy odor in the long run, thus affecting the washing effect. Although users can manually open the emergency drain valve to discharge the water, this process is cumbersome and easily neglected. This paper designs and develops an automatic drainage device based on ESP32 microcontroller, which realizes the automatic drainage of water inside the washing machine through the cooperative work of water pump and solenoid valve. It is designed as a non-destructive modification without affecting the product warranty. Promoting this device can effectively solve the problem of residual water accumulation in existing drum washing machines and improve the user experience.