The Ontario Building Code | Underground Ducts
220.127.116.11. Underground Ducts
(1) Underground ducts shall,
(a) be constructed and installed with a slope to provide interior drainage to all low points,
(b) not be connected directly to a sewer, and
(c) be installed and constructed of materials in conformance with ASHRAE Handbooks, SMACNA Manuals and the HRAI Digest.
(2) A clean-out or pump-out connection shall be provided in an underground duct system at every low point of the duct system.