Ill. Admin. Code tit. 77, § 890.370 - Prohibited Joints and Connections in Drainage Systems
Drainage System. Any fitting or connection which has an enlargement, chamber, or recess with a ledge, shoulder, or reduction of pipe area that offers an obstruction to flow through the drain is prohibited. No fitting or connection that obstructs flow shall be used. In existing buildings only a flow control valve or device may be connected to the fixture drain and shall not be considered as an obstruction. The enlargement of a three (3) inch closet bend or stub to four (4) inches shall not be considered an obstruction.
Notes
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