: Are toilet vents and sink vents the same size? During remodeling they changed places with the toilet and sink. : Now the toilet is vented by the old sink vent and the new sink has one of those under the cabinet plastic vents. : Nothing seems to drain properly now. Could the vent sizes be the problem?:Without being more specific on sizes and location of the fixtures in conjunction with your layout,It would be hard to say.Also depending on the region you live in and what codes are followed.Im in middle Tenn and here the smallest acceptable vent allowed for a water closet is 1 1/2 although the standard is usually 2 with at least one main vent of 3 or greater located in the structure.When you say it drains poorly are you referring to one fixture or the entire group?
