Kitchen Sink Plumbing Diagram: Supply, Drain, and Rough-In Guide

A kitchen sink plumbing diagram is your planning document for any kitchen renovation that touches the sink area. Whether you’re replacing a sink, adding a garbage disposal, or relocating the sink in a full kitchen remodel, a clear sink plumbing diagram prevents costly mistakes during rough-in. The kitchen sink drain plumbing diagram shows how the drain, trap, and waste arm connect to the wall drain. A kitchen plumbing diagram covers the full supply and drain system for the space. A kitchen sink plumbing rough in diagram sets the exact pipe positions needed before walls close. Getting any of these wrong means rework — and rework in a finished kitchen is expensive.

Kitchen Sink Plumbing Diagram: What It Shows

Supply Side

The supply side of a kitchen sink plumbing layout shows the hot and cold water supply stub-outs coming up through the cabinet floor or out of the back wall. Standard kitchen sink supply rough-in places stub-outs 18 to 20 inches above the finished floor, centered under the sink, 8 inches apart (4 inches each side of the drain centerline). These stub-outs terminate in either compression angle stops or push-connect shut-offs. From the shut-offs, braided stainless or flexible supply lines connect to the faucet body above.

Drain Side

The kitchen sink drain plumbing layout shows the drain basket at the bottom of each bowl, a slip-joint P-trap on each drain, and the waste arm that connects the trap to the wall drain. For a double-bowl sink, a continuous waste configuration uses a center fitting that connects both drains to a single P-trap. An end-outlet configuration plumbs each bowl separately. The wall drain stub-out for the kitchen sink is typically a 2-inch drain set 18 to 20 inches above the finished floor. The P-trap must sit below the sink bottom — typically 8 to 10 inches above finished floor — so the waste arm angles down toward the wall drain at the required slope.

Rough-In Dimensions for Kitchen Sink Plumbing

A kitchen sink plumbing rough in diagram establishes four key dimensions before the cabinet goes in:

• Drain stub-out height: 18 to 20 inches above finished floor
• Drain stub-out horizontal position: centered under the sink location
• Supply stub-out height: 18 to 20 inches above finished floor
• Supply stub-out spacing: 8 inches apart (4 inches each side of drain center)

These are starting reference points — always confirm the dimensions against the specific sink and faucet you’re installing. Farmhouse apron sinks, for instance, often require the drain centered much lower than a drop-in bowl because the sink bottom sits lower in the cabinet.

Garbage Disposal in the Kitchen Sink Drain Diagram

When a garbage disposal is included, the drain plumbing diagram shows the disposal mounting flange in the drain, the disposal body below, and the discharge tube exiting the disposal side. The discharge connects to a P-trap that then runs to the wall drain. If a dishwasher is present, its drain line connects to a high loop under the counter before connecting to the disposal inlet port (or directly to the drain arm in some configurations). The high loop prevents siphoning from the dishwasher drain back into the tub.

Reading and Using Your Plumbing Rough-In Diagram

When working from a kitchen plumbing diagram during a renovation, mark the drain and supply stub-out locations on the framing and subfloor before the cabinet installer arrives. The cabinet box must have a cutout for supply and drain access, and the dimensions must match. Discovering a dimension mismatch after the cabinet is installed — and you need a 2-inch hole where there’s a solid cabinet panel — is the expensive kind of problem that a rough-in diagram prevents.