How to Unblock a Drain When There Is Standing Water Present

Standing water in your sink, shower, or laundry tub is a sure sign of a blocked drain. In most cases, the blockage is close to the surface and can be cleared with a few basic tools and a bit of patience — no plumber required. However, some situations do need a licensed professional, so read on to know the difference.

Safety First

Before you start, keep these points in mind:

• Never mix drain-clearing chemicals — combining products (especially bleach and caustic soda) can cause dangerous reactions.
• Wear rubber gloves and eye protection when handling any chemical drain cleaner.
• If the standing water is in a toilet or appears to be coming up from multiple fixtures at once, stop and call a professional immediately — this may indicate a blocked main drain or sewer line.
• Check WorkSafe NZ guidance if you're ever unsure about handling hazardous household chemicals.

What You'll Need

Gather these items before you begin:

• Rubber gloves and safety glasses
• A cup plunger (for sinks and showers) or a flange plunger (for toilets)
• A bucket and old towels
• A drain snake or flexible drain auger (available at Bunnings or Mitre 10)
• Baking soda and white vinegar (natural option)
• A chemical drain cleaner (as a last resort)

Step 1 — Remove as Much Standing Water as Possible

Bail out the standing water using a cup or small bucket into a separate bucket or toilet. This makes it easier to see what you're working with and reduces mess. Leave just enough water to cover the base of the plunger cup — you need a water seal for the plunger to work effectively.

Step 2 — Try Plunging First

Plunging is almost always your best first move. It's fast, chemical-free, and works well on soft blockages like hair, soap scum, and food scraps.

1. Place the plunger cup firmly over the drain opening, ensuring a good seal.
2. For sinks with an overflow hole, block it with a wet cloth — this forces pressure down into the drain rather than escaping upward.
3. Push down firmly and pull up sharply, repeating 10–15 times in a steady rhythm.
4. Lift the plunger and check if the water drains. Repeat if needed.

Step 3 — Clear the Drain Cover and P-Trap

If plunging doesn't work, the blockage may be sitting just below the drain cover or in the P-trap (the curved pipe section under the sink).

• Remove the drain cover (usually a simple twist or lift) and use gloved fingers or a bent wire hook to pull out any hair or debris.
• Under a sink, place a bucket beneath the P-trap, unscrew the slip-joint nuts by hand, and remove the trap. Clean it out, then refit it hand-tight (no tools needed for plastic traps).

Step 4 — Use a Drain Snake

A drain snake (also called a hand auger) is ideal for blockages deeper in the pipe that plunging can't reach.

1. Feed the snake into the drain opening, turning the handle clockwise as you push.
2. When you feel resistance, you've hit the blockage — keep rotating to break it up or hook it so you can pull it out.
3. Withdraw the snake slowly, wiping it clean as you go.
4. Flush the drain with hot water to clear any remaining debris.

Step 5 — Try a Natural or Chemical Drain Cleaner

If mechanical methods haven't fully cleared the drain, a cleaner can help dissolve remaining residue.

Avoid using chemical cleaners in fully blocked drains with standing water — the chemicals can splash back and cause burns, and they may not reach the blockage effectively anyway. Always follow the manufacturer's instructions.

Step 6 — Flush and Test

Once the blockage clears, run hot water for two to three minutes to flush the pipe fully. Check under the sink for any leaks if you removed the P-trap.

Preventing Future Blockages

• Fit a hair catcher over shower and bath drains.
• Never pour cooking fats or oils down the kitchen sink.
• Run hot water down the drain for 30 seconds after each use.
• Do a monthly baking soda and vinegar flush as routine maintenance.

When to Call a Professional

Some drain problems are beyond DIY — and in New Zealand, certain drainage work is restricted to licensed tradespeople. Call a professional drain cleaner or registered plumber if:

• Multiple fixtures (toilet, sink, shower) are backing up at the same time — this suggests a main drain or sewer blockage.
• You can smell sewage or notice gurgling sounds from other fixtures.
• The blockage keeps returning despite repeated clearing.
• You suspect a collapsed or damaged pipe — common in older NZ homes with clay or cast-iron drainage.
• Any work involves connecting to or modifying the drainage system — this is restricted work under the Plumbers, Gasfitters and Drainlayers Board (PGDB) and must be carried out by a licensed drainlayer.

For rental properties, landlords also have obligations under the Healthy Homes Standards to maintain drainage in good working order.

You can find qualified, local drain cleaners and plumbers on tradedirectory.co.nz.

Sources & Further Reading

• Plumbers, Gasfitters and Drainlayers Board — Licensed tradespeople
• MBIE Building Performance — NZ Building Code drainage requirements
• WorkSafe NZ — Safe handling of hazardous substances
• Tenancy Services — Healthy Homes Standards
• BRANZ — Building research and best practice