The answer to 'how to maintain backflow preventer' is to regularly inspect, test, and clean the device. Backflow preventers are critical safety devices that keep contaminated water from flowing back into the clean water supply, so proper maintenance is essential.
You should have a certified backflow technician inspect and test the device at least once per year, or more often if required by local regulations. They will check for any cracks, leaks, or other damage, and ensure the device is working properly. Additionally, you should visually inspect the backflow preventer monthly for any signs of problems.