Sanitary Tee Got your back

Drain pipe from sink, tub, toilet or shower is not permitted to drain into a sanitary tee in a horizontal position (On its back). This fitting must be a combination Y and 1/8 bend.

A combination Y and 1/8 bend. Is the correct fitting used to connect a vertical drain to a horizontal drain or a Horizontal drain to a horizontal drain.

http://www.co.lincoln.or.us/sites/default/files/fileattachments/planning_amp_development/page/722/plumbing_guide_2015_-_helpful_hints_residential_construction.pdf