The Ontario Building Code | Vents for Sanitary Sewage Sumps or Tanks, Dilution Tanks and Macerating Toilet Systems
7.5.7.7. vents for sanitary Sewage Sumps or Tanks, Dilution Tanks and Macerating Toilet Systems
(1) Except as provided in Sentences (2) and (3), the minimum size of the vent pipe for a sanitary sewage sump or tank, or dilution tank shall be one size smaller than the sizeof the largest branch or fixture drain draining to the sump or tank.
(2) The size of every vent pipe for a sanitary sewage sump or tank, or dilution tank shall be not less than 2 in., but need not be greater than 4 in.
(3) The size of every vent pipe for a macerating toilet system with a sump or tank shall be not less than 1 ½ in.