Spot the Violation

PlumbingBackflow & cross-connectionsLevel 22018 UPC

Kitchen sink base with dishwasher

Kitchen sink base cabinet with its doors swung open, seen from standing height. On the countertop, a double-bowl stainless sink has a pull-down faucet at the back center and a soap pump in the right rear hole; there is no other fitting on the deck. A stainless dishwasher sits in the opening to the left of the sink base. Under the sink, a food waste disposer hangs from the right bowl and a white plastic tubular P-trap serves both bowls. A gray ribbed dishwasher drain hose comes through a hole low in the left cabinet side, climbs the side wall, is held in a plastic strap screwed to the underside of the countertop, and drops to the dishwasher inlet on the disposer, where it is clamped. Chrome angle stops with braided supply lines feed the faucet and the dishwasher, and the disposer cord plugs into a receptacle on the back wall.
Kitchen sink base, doors open, next to the dishwasher

What's wrong here?

  1. Nothing. This installation is compliant
  2. There is no air gap fitting on the sink deck, so the dishwasher drain is not protected
  3. A dishwasher may not discharge into a food waste disposer
  4. The dishwasher drain needs its own trap before it joins the disposer
Start this drill
Show the answer and the code reference

The answer

Nothing is wrong. In Minnesota a domestic dishwasher may discharge to the disposer through a drain line fastened as high as possible under the countertop instead of through a deck-mounted air gap.

Correct choice: 1. Nothing. This installation is compliant

The 2018 UPC 807.4 as published requires a listed air gap fitting, set with its flood-level mark at or above the sink's flood rim, between a domestic dishwasher and the drainage system or disposer. Minnesota amended 807.4 in the 2020 Minnesota Plumbing Code (effective Dec. 17, 2021) to restore the high loop as an alternative: the discharge line may instead be run as high as possible under the countertop and securely fastened. Here the hose rises from the cabinet floor, is strapped to the underside of the counter, and drops to the disposer inlet, so it complies. The high loop keeps sink water from running back into the dishwasher; it is not a true air gap, which is why the model code does not accept it. A local ordinance or the dishwasher's installation instructions can still call for an air gap.

How to fix it

No correction needed. Before signing off, confirm the strap holds the loop tight to the underside of the counter, the hose is clamped at the disposer, and the disposer's dishwasher knockout plug was removed.

Code references

  • Minn. Rules 4714.0807 — Domestic Dishwashing Machine (Minnesota amendment to UPC 807.4)

    Minnesota's version of 807.4 does not allow a domestic dishwasher to connect directly to the drainage system or a food waste disposer unless its discharge passes through an approved dishwasher air gap fitting or the discharge line is run as high as possible under the countertop and securely fastened.

    Drills citing 4714.0807

  • UPC 2018 807.4 — Domestic Dishwashing Machine

    As published, the UPC does not allow a domestic dishwasher to be connected directly to a drainage system or food waste disposer without a listed air gap fitting on its discharge side, installed with its flood-level marking at or above the flood level of the sink or drainboard, whichever is higher.

    Drills citing 807.4

Minnesota

MN status unverifiedConfidence: medium

Minnesota adopts the 2018 Uniform Plumbing Code with Minnesota amendments as the Minnesota Plumbing Code (Minn. Rules ch. 4714, effective Dec. 17, 2021). Search-result excerpts of Minn. Rules 4714.0807 and Minnesota industry summaries (Structure Tech, Housing First Minnesota) report that Minnesota amended UPC 807.4 so a domestic dishwasher may discharge either through an approved air gap fitting or through a discharge line run as high as possible under the countertop and securely fastened. The 2016-2021 Minnesota code required the air gap. The amended text itself could not be read for this drill. The compliant answer depends on this amendment: under the model UPC 807.4 this drawing is a violation.

About the Minnesota Plumbing Code

Citation under review. The drill's compliant answer rests entirely on the reported Minnesota amendment to UPC 807.4 (Minn. Rules 4714.0807), which the author and the verifier could confirm only through search-result excerpts; revisor.mn.gov was blocked. Confirm in the published rule: (1) the high-loop alternative exists ('as high as possible under the countertop' and 'securely fastened' or equivalent), (2) it applies when the dishwasher discharges to a food waste disposer, and (3) the heading of 4714.0807. If Minnesota still requires a listed air gap, make this a violation drill (choice: no air gap fitting) and drop the high-loop explanation.

Why the other choices are wrong

  • There is no air gap fitting on the sink deck, so the dishwasher drain is not protected. The model UPC 807.4 does require a listed air gap, but Minnesota amended it: a residential dishwasher may instead have its discharge line run as high as possible under the countertop and securely fastened, which is what the strapped high loop here does.
  • A dishwasher may not discharge into a food waste disposer. 807.4, in both the model and the Minnesota versions, lets a domestic dishwasher discharge to the disposer's dishwasher inlet; the condition is that the discharge passes through an air gap or, in Minnesota, a fastened high loop.
  • The dishwasher drain needs its own trap before it joins the disposer. The dishwasher discharges through the sink's P-trap. Adding a second trap in series would double-trap the line, which the UPC prohibits.
Code complianceLevel 2 · Journeyman#dishwasher#air gap#high loop#food waste disposer#Minnesota amendment#kitchen

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