The piping of a central vacuum (fluid suction) system shall be of corrosion-resistant material with a smooth interior surface. A branch shall not be less than 1/2 inch (12 mm) nominal pipe size for one outlet and shall be sized in accordance with the number of vacuum outlets. A main shall not be less than 1 inch (25 mm) nominal pipe size. The pipe sizing shall be increased in accordance with the manufacturer's instructions as stations are increased. For the purposes of inspection, maintenance and replacement, all piping shall have cleanout facilities on mains and branches. Access shall be provided to such cleanout facilities.