Kitchen Remodel Plumbing Checklist — Every Step Before, During, and After

The sink drives the drain location, which is the hardest pipe to move. Drain lines need a 1/4-inch-per-foot slope to the main stack, and that slope determines the maximum distance you can move the sink from the existing drain. Moving a sink more than 5–6 feet typically requires opening the floor to reroute the drain. An undermount sink, farmhouse sink, or vessel sink each require different cabinet and countertop preparations. Make this decision first — everything else follows from it. If you're relocating the sink, get your plumber's input on feasibility before the cabinet order locks in.

Beyond the sink, identify every appliance that needs plumbing: dishwasher (hot water supply + drain), refrigerator with ice maker/water dispenser (cold water supply), pot filler (cold water supply in the wall behind the stove), instant hot water dispenser (hot/cold supply + electrical), water filtration system (cold supply + drain for reverse osmosis waste). Each requires a supply line run to a specific cabinet or wall location. Mark these on the kitchen plan and share with your plumber before rough-in.

Any plumbing work involving moving supply or drain lines, adding new fixtures, or modifying gas lines requires a permit in most jurisdictions. Your licensed plumber pulls the permit — not you, not the general contractor (unless they hold a plumbing license). The permit ensures the work is inspected for code compliance. Starting work without a permit risks fines, stop-work orders, and having to tear out and redo non-compliant work. Permit cost: $75–$300. Processing time: 1–10 business days depending on your jurisdiction.

Plumbing costs in a kitchen remodel range from $500 (replacing fixtures in the same locations) to $5,000+ (moving the sink to an island, adding a pot filler, rerouting the main drain). The plumber needs the kitchen plan with fixture and appliance locations to provide an accurate estimate. Get this estimate before committing to the overall budget — plumbing surprises mid-project are the most common source of cost overruns in kitchen remodels.

Before any cabinets, countertops, or walls come out, the plumber caps all supply lines and plugs all drain connections to prevent water damage during demo. This takes 1–2 hours and prevents the 'accidentally hit a pipe during demo' disaster. The plumber should also identify the main shut-off location and verify it works — if the main shut-off is frozen or faulty, that's a problem to fix before demo, not during a flooding emergency.

PEX supply lines route through open wall cavities and under the subfloor to each fixture location: sink (hot + cold), dishwasher (hot), refrigerator ice maker (cold), pot filler (cold in-wall), and any other water-using appliances. Each run terminates with a stub-out and shut-off valve at the correct height and location for the fixture. The plumber references the cabinet plans to position stub-outs where they'll be accessible inside the cabinet, not behind a drawer box or trapped behind a fixed shelf.

The drain line is the most constrained element — it needs a continuous slope of 1/4 inch per foot to the main stack or building drain. If the sink moved, the drain moves. If the drain moved more than a few feet, the vent may need to be rerouted too. Kitchen sinks require a 2-inch drain line and a 1.5-inch vent. Island sinks need special venting (air admittance valve, loop vent, or island vent) because there's no wall to run a conventional vent to the roof. This is where experienced plumbers earn their money — drain/vent routing is the most code-intensive part of kitchen plumbing.

If you're adding a gas range or moving an existing one, a gas line must be run to the new location. Gas line work requires a specific plumbing or gas fitting license in most jurisdictions and always requires a permit and pressure test inspection. Black iron pipe or CSST (corrugated stainless steel tubing) are the two approved materials. The gas line terminates with a shut-off valve behind the range. Cost: $200–$800 for a new gas line run, depending on distance and material. Never attempt gas line work yourself — a leak is a life-safety hazard.

The building inspector needs to see all supply, drain, vent, and gas lines before walls and floors are closed up. The plumber schedules this inspection — it typically happens within 2–5 business days of the request. The inspector verifies pipe sizing, slope, vent connections, material approvals, and support/hanging. If the rough-in fails inspection, repairs are relatively easy with walls open. If walls are closed before inspection, the inspector can require you to open them again. Never skip this step.

Undermount sinks are often set before the countertop is templated and installed. Drop-in and farmhouse sinks install after the countertop. The plumber connects the faucet, P-trap, tailpiece, and drain to the rough-in stub-outs. For undermount sinks with garbage disposals, the plumber installs the disposal mounting ring and wires the disposal at this stage. This is also when the hot and cold supply lines connect to the faucet shut-off valves.

The dishwasher connects to the hot water supply via a braided stainless supply line, drains through a high loop or air gap device into the garbage disposal or sink tailpiece, and requires a dedicated electrical circuit (usually hardwired or plug-in). The drain hose must loop up to the underside of the countertop (high loop) or connect through an air gap fitting mounted on the sink or countertop — this prevents wastewater from the sink or disposal from backflowing into the dishwasher. Code requirements for high loop vs. air gap vary by jurisdiction.

A 1/4-inch braided stainless or copper supply line runs from a saddle valve or dedicated shut-off on the cold water supply to the refrigerator location. Leave enough slack (6–8 feet of coiled line behind the refrigerator) so the fridge can be pulled out for cleaning and service without disconnecting. Use braided stainless supply lines — not the plastic tubing included with some refrigerators, which becomes brittle and cracks after 5–7 years. A quarter-turn shut-off valve at the supply end is essential.

The disposal mounts to the sink's drain flange and connects to the P-trap and branch drain. If a dishwasher connects to the disposal, the plumber knocks out the dishwasher drain plug inside the disposal inlet. The disposal needs a dedicated 15-amp or 20-amp electrical circuit — either hardwired to a wall switch or connected to a switched outlet under the sink. Most 1/2 HP disposals handle typical household use; 3/4 HP or 1 HP models handle tougher waste and jam less frequently.

Under-sink reverse osmosis (RO) systems or carbon block filters connect to the cold water supply via a tee fitting and have a drain line for waste water (RO systems discharge 2–4 gallons of waste per gallon of filtered water). The filtered water feeds a dedicated faucet mounted on the sink or countertop — this requires an additional hole if not planned for during countertop fabrication. Whole-house filters install on the main water line, not under the sink. Plan the faucet hole during countertop templating.

Turn on every faucet (hot and cold), run the dishwasher through a full cycle, check the ice maker connection, and run the garbage disposal with water flowing. Check under the sink and behind the dishwasher for drips at every connection point. Small drips at compression fittings often don't show up until 5–10 minutes of continuous use. Lay paper towels under connections to make slow drips visible. Finding a drip now costs $0 to fix; finding one after the floor is finished costs hundreds.

Fill the sink and release — the drain should empty a full basin in under 30 seconds. Slow draining indicates incorrect slope, a restriction in the line, or an improperly connected vent. Run the dishwasher and verify it drains completely without backing up into the sink. Test the garbage disposal with water running — it should drain as fast as the disposal grinds. Sluggish drains during testing will only get worse with daily use.

Turn off each shut-off valve (sink hot, sink cold, dishwasher, ice maker) and verify that water stops flowing to that fixture. Then open them fully and verify full flow returns. Shut-off valves that don't fully close are useless in an emergency. Quarter-turn ball valves are the most reliable — if the plumber installed multi-turn gate valves, request an upgrade to ball valves before final payment.

The final inspection verifies that all fixtures are properly connected, drains function, vents are complete, and the installation matches the permitted plans. The inspector may run water, check trap seals, verify air gaps, and test gas connections with a leak detector. A passed final inspection closes the permit and confirms the work is code-compliant. Keep the inspection report with your home records — you'll need it for resale disclosure.