The Ontario Building Code | Serving Water Closets

7.4.9.2. Serving water Closets

(1) The size of every drainage pipe that serves a water closet shall be at least 3 in.

(2) The size of every horizontal drainage pipe downstream of the third water closet fixture drainconnection shall be at least 4 in.

(3) The size of every soilstack that serves more than six water closets shall be at least 4 in.

(4) The size of the discharge pipe serving a macerating toilet system shall be at least ¾ in.

(5) No vertical leg of the drainage pipe from a water closet or other fixture that has an integral siphonic flushing action shall exceed 1 000 mm.