(1) Except as permitted in Sentences (2) and (3), 90° elbows of 4 in. size or less that have a centre-line radius that is less than the size of the pipe shall not be used to join two soil or waste pipes.
(2) 90° elbows of 4 in. size or less in sanitary drainage systems may be used,
(a) to change the direction of piping from horizontal to vertical, in the direction of flow,
(b) where a trap arm enters a wall, or
(c) to connect trap arms as permitted by Sentence 7.5.6.3. (2).
(3) A 90° elbow that is part of the pre-engineered wastewater heat recovery system is permitted to have a centre-line radius that is less than the size of the pipe.