Plumbing Installation Starts With a Code-Compliant Plan A reliable plumbing installation begins with a clear layout, correctly sized water and drain lines, proper venting, and testing before walls are closed. For a new home, the work usually moves through four stages: Plan fixture locations and confirm local permit and code requirements. Rough in drain, waste, vent, and water supply piping. Pressure-test the system and correct leaks before inspection. Install fixtures, applia