we moved into our house three years ago. The drains were new, and now three years after I'm interested if we should cleen them.
Normal modern drain installations do not require any regular cleaning. If you notice a clog/slowdown or gurgling, a targeted cleaning may help. But if your concern is buildup of material inside of drain/waste/vent pipes, this is rarely a concern. Sometimes after 50-100 years there can be enough buildup to cause a problem. But preemptive cleaning of drains is not typically worth it.