Methods of substantially removing a restriction from a drain pipe system include the steps of introducing a cleaning composition containing a non-caustic drain opening active to the pipe system, activating the cleaning composition by adding a sufficient amount of liquid to the drain pipe system while maintaining a flow-through state through the pipe system, allowing the drain opening active to remain in contact with the restriction for a sufficient time to substantially degrade the restriction, and rinsing the drain opening active from the pipe system. The water flow rate through the pipe system is improved by at least 0.7 liters/minute after 16 hours of the drain opening active contacting the restriction. These methods are effective for both clogged and slow-running drains.