The Ontario Building Code | No Reduction in Size
188.8.131.52. No Reduction in Size
(1) Except as permitted in Sentence (3), no drainage pipe that is of minimum size required by this Part for the purpose for which it is installed shall be so connected as to drain to other drainage pipe of lesser size.
(3) A sanitary drainage pipe may be connected to a pre-engineered waste water heat recovery system that incorporates piping of a lesser size than required by Sentence (1) provided that it does not convey sewage,
(a) from a sanitary unit, or
(b) that contains solids.