How Do I Clear a Blocked Kitchen Sink?

A blocked kitchen sink is one of the most common plumbing problems in Kiwi homes. The good news is that many blockages can be cleared with basic tools and a bit of know-how — no licence required. Here's how to tackle it safely and effectively.

Why Kitchen Sinks Block Up

Kitchen sink blockages are almost always caused by a build-up of fats, oils, and grease (FOG), food scraps, soap scum, or a combination of all three. Over time these coat the inside of your pipes and trap debris until water can no longer drain freely. Homes with older galvanised or narrow pipework can be more prone to recurring blockages.

What You'll Need

Before you start, gather the following:

• Cup plunger (the flat-bottomed type, not a toilet plunger)
• Old towels or a bucket
• Rubber gloves
• Adjustable pliers or a pipe wrench
• A bottle brush or flexible drain brush
• Baking soda and white vinegar (optional, natural method)
• Chemical drain cleaner (use sparingly — see caution below)

Step 1 — Try Boiling Water First

For a partial blockage caused by grease, the simplest fix is often the best. Carefully pour a full jug of just-boiled water slowly down the drain in two or three stages, allowing it to work between pours. This can melt and shift fatty build-up without any chemicals or tools.

Safety note: Don't use boiling water if you have PVC (plastic) drain pipes under the sink, as repeated exposure to very hot water can soften joints over time. Use hot tap water instead.

Step 2 — Use a Plunger

If boiling water doesn't do the trick, reach for the plunger.

1. Remove any standing water from the sink until there's just enough to cover the plunger cup.
2. Block the overflow hole (if your sink has one) with a wet cloth to create proper suction.
3. Place the plunger firmly over the drain and push down and pull up rapidly 10–15 times.
4. Lift the plunger sharply on the final pull — you should hear a gurgle as the blockage shifts.
5. Run hot water to flush the drain clear.

Repeat two or three times if needed.

Step 3 — Baking Soda and Vinegar

This is a gentler, eco-friendly option that works well on mild grease blockages:

1. Pour half a cup of baking soda down the drain.
2. Follow with half a cup of white vinegar.
3. Cover the drain and leave for 15–30 minutes while it fizzes.
4. Flush with hot water.

This won't shift a solid blockage but is great for maintenance and mild slow drains.

Step 4 — Clear the P-Trap

If plunging hasn't worked, the blockage is likely sitting in the P-trap — the curved section of pipe directly under the sink. This is straightforward to remove and clean.

1. Place a bucket under the P-trap to catch water and debris.
2. Unscrew the slip-joint nuts by hand or with pliers (wrap the jaws with tape to avoid scratching).
3. Remove the P-trap and empty the contents into the bucket.
4. Use a bottle brush to scrub the inside of the trap clean.
5. Check the pipe leading into the wall for any visible blockage and clear it with a flexible brush or drain snake if needed.
6. Refit the P-trap, hand-tighten the nuts, and run water to check for leaks.

Tip: While the trap is off, inspect the rubber washers inside the slip-joint nuts. If they're cracked or flattened, replace them — they're inexpensive and available at Mitre 10 or Bunnings.

Step 5 — Use a Drain Snake (Auger)

If the blockage is further down the line, a hand drain snake (also called a plumber's auger) can reach it. Feed the cable into the drain pipe, turn the handle clockwise to drive it forward, and work it back and forth to break up or hook the blockage. Drain snakes are available to hire or buy from most hardware stores.

Chemical Drain Cleaners — Use With Caution

Products like caustic soda-based drain cleaners are available at supermarkets and hardware stores. They can be effective but come with real downsides:

If you do use a chemical cleaner, always follow the label instructions, wear gloves and eye protection, and never mix products. Check guidance from WorkSafe NZ on handling hazardous household chemicals safely.

Preventing Future Blockages

• Never pour cooking oil or grease down the sink — let it cool and dispose of it in the bin.
• Use a sink strainer to catch food scraps.
• Flush the drain with hot water after washing greasy dishes.
• Do a baking soda and vinegar flush monthly as maintenance.

When to Call a Professional

Some situations are beyond a DIY fix. Call a licensed plumber if:

• Multiple drains in your home are blocked at the same time (this suggests a problem in the main drain or sewer line).
• You've cleared the P-trap and snaked the pipe but the drain is still slow or blocked.
• You notice foul smells, gurgling from other fixtures, or water backing up into other drains — signs of a deeper drain or venting issue.
• Your pipes are old and you're concerned about their condition.

Drainlaying and work on the main sewer connection is restricted work under the Plumbers, Gasfitters and Drainlayers Board (PGDB) regulations and must be carried out by a licensed tradesperson. Attempting this work yourself could result in fines and may affect your home insurance.

You can find a qualified local plumber or drainlayer on tradedirectory.co.nz.

Sources & Further Reading

• Plumbers, Gasfitters and Drainlayers Board — Licensed tradespeople
• BRANZ — Home maintenance guidance
• WorkSafe NZ — Hazardous substances safety
• MBIE Building Performance — NZ Building Code
• Tenancy Services — Healthy Homes maintenance obligations