Kitchen sink drop in the basement ceiling
What's wrong here?
- The vertical drop from the kitchen enters the horizontal drain through a sanitary tee
- The horizontal drain may not join the stack through a sanitary tee
- A line serving a kitchen sink needs a cleanout at its upper end
- Nothing. This installation is compliant
Show the answer and the code reference
The answer
The 2 in. kitchen drop turns from vertical to horizontal through a sanitary tee laid on its back. A vertical-to-horizontal change must be made with a wye, a combination wye and 1/8 bend, or another approved fitting of equivalent sweep.
Correct choice: 1. The vertical drop from the kitchen enters the horizontal drain through a sanitary tee
UPC 706.4 says vertical drainage lines connecting with horizontal drainage lines must enter through 45-degree wye branches, combination wye and 1/8 bend branches, or other approved fittings of equivalent sweep. The sanitary tee is not on that list, even though 706.2 allows it where a horizontal line enters a vertical stack. Waste falling down the drop hits the bottom of the horizontal line almost head-on, so it splashes back up the run toward the cleanout and slows the flow, which leads to buildup and stoppages. Note the contrast in this picture: the same fitting is legal at the stack and illegal at the drop.
How to fix it
Cut out the tee and install a 3 x 2 combination wye and 1/8 bend (or a wye with a 1/8 bend on the branch) set with its branch rolled up to vertical and sweeping toward the stack. Keep the run sloped at least 1/4 in. per ft toward the stack.
Code references
UPC 2018 706.4 — Vertical to Horizontal
Vertical drainage lines connecting with horizontal drainage lines are to enter through 45-degree wye branches, combination wye and 1/8 bend branches, or other approved fittings of equivalent sweep.
Drills citing 706.4UPC 2018 706.2 — Horizontal to Vertical
Horizontal drainage lines connecting with a vertical stack may enter through 45-degree wye branches, combination wye and 1/8 bend branches, sanitary tee or sanitary tapped tee branches, or other approved fittings of equivalent sweep.
Drills citing 706.2
Minnesota
Minnesota adopts the 2018 Uniform Plumbing Code with Minnesota amendments as the Minnesota Plumbing Code (Minn. Rules ch. 4714, effective Dec. 17, 2021). No Minnesota amendment to 706.4 is known; check ch. 4714 before relying on it. Search-result excerpts point to a Minnesota Plumbing Board interpretation (reported as PB0183, October 2024) that allows long-sweep and short-sweep quarter bends and listed long-pattern fittings for horizontal-to-horizontal and vertical-to-horizontal changes; it could not be read. Even if accurate, it widens the bends allowed and does not add the sanitary tee.
About the Minnesota Plumbing CodeCitation under review. Confirm the Minnesota Plumbing Board interpretation in the Minnesota note (reported as PB0183, Oct. 15, 2024) and its wording on quarter bends for 706.3/706.4; it comes from search-result snippets only. Also confirm whether Minnesota's amended 707.4 (apparently Minn. Rules 4714.0707) keeps cleanouts for kitchen sink lines above the lowest floor. The cleanout distractor no longer depends on it because a cleanout is drawn, and the answer rests on the model 706.4 text.
Why the other choices are wrong
- The horizontal drain may not join the stack through a sanitary tee. UPC 706.2 lists the sanitary tee for horizontal-to-vertical connections. The tee at the stack is correct; the problem is the tee where flow turns from vertical to horizontal.
- A line serving a kitchen sink needs a cleanout at its upper end. Whether or not this line needs one (Minnesota's amended 707.4 is reported to keep cleanouts for kitchen sink lines even above the lowest floor), it has one: the threaded plug at the left end of the run is an upper-terminal cleanout.
- Nothing. This installation is compliant. A sanitary tee set on its back so that a vertical line enters a horizontal drain is not one of the fittings 706.4 permits for a vertical-to-horizontal change of direction.