How to Fix a Slow Draining Bath Without Removing the Trap

A slow draining bath is one of the most common household plumbing nuisances in New Zealand, and the good news is you can usually fix it yourself without removing the trap or calling a plumber. In most cases, the culprit is a build-up of hair, soap scum, and body oils sitting just below the drain cover — well within reach of a few simple tools and techniques.

What Causes a Slow Bath Drain?

Before you start, it helps to understand what you're dealing with. The most common causes of a slow bath drain are:

• Hair accumulation just below the drain strainer or pop-up plug mechanism
• Soap scum and body oil coating the inside of the drain pipe
• A partially blocked overflow channel (the small hole near the top of the bath)
• A worn or poorly seating pop-up plug that doesn't open fully

Rarely, the blockage may be deeper in the waste pipe or trap itself — but start with the simple fixes first.

Step 1: Remove and Clean the Drain Cover

Most bath drain covers either unscrew (one central screw) or simply lift or twist off. Remove it and set it aside.

Once the cover is off, use a torch to look into the drain. You'll almost certainly see a clump of hair and soap residue sitting on top of or just below the drain grate. Use a pair of needle-nose pliers, a purpose-made drain snake hook, or even a bent wire coat hanger to pull the gunk out. This step alone often solves the problem entirely.

Clean the drain cover itself with an old toothbrush and warm soapy water before replacing it.

Step 2: Try a Drain Cleaning Tool

If pulling out visible debris doesn't fully restore drainage, a plastic drain cleaning strip (sometimes called a Zip-It or hair snake) is a cheap and effective tool available at Bunnings or Mitre 10. These flexible plastic strips have barbed edges that grab hair as you pull them back out.

Insert the strip into the drain as far as it will go, rotate it slightly, then pull it back out slowly. Repeat a few times, clearing the debris off the strip between each pass. You don't need to remove the trap to do this — the strip works within the accessible section of pipe above the trap.

Step 3: Use Boiling or Very Hot Water

Once you've removed the physical debris, flush the drain with very hot (near-boiling) water poured slowly and steadily. This helps melt and shift soap scum coating the pipe walls. Do this two or three times with a minute or two between pours.

Caution: Don't pour boiling water directly into older acrylic or fibreglass baths, as it can cause cracking or warping. Use hot tap water (around 60–70°C) instead, or let boiling water cool for a minute first.

Step 4: Baking Soda and Vinegar Flush

For stubborn soap scum, a baking soda and white vinegar flush is a safe, chemical-free option:

1. Pour half a cup of baking soda directly into the drain.
2. Follow with half a cup of white vinegar.
3. Cover the drain opening with a cloth or plug to direct the fizzing action downward.
4. Leave for 15–30 minutes.
5. Flush with hot water.

This method is gentle on pipes and safe for septic systems, which are common in rural New Zealand.

Step 5: Check the Overflow

Many baths have an overflow plate — a small cover near the top of the bath that hides the overflow drain. Hair and soap scum can accumulate here too, restricting airflow and slowing drainage. Unscrew the overflow plate, clean out any debris, and replace it. This is often overlooked but can make a noticeable difference.

Step 6: Use a Plunger

If the drain is still slow, a cup plunger (not a flange plunger, which is for toilets) can help dislodge a partial blockage further down. Block the overflow opening with a wet cloth first — this is important, as it creates the necessary pressure. Place the plunger over the drain, add enough water to cover the cup, and plunge firmly 10–15 times. Remove the plunger quickly on the last pull to help dislodge the blockage.

What About Chemical Drain Cleaners?

Caustic drain cleaners are available at hardware stores, but use them with caution. They can damage older pipes, are harmful to the environment, and may not be suitable for septic tanks. Always follow the manufacturer's instructions and wear gloves and eye protection. WorkSafe NZ recommends proper PPE when handling caustic chemicals at home.

Preventing Future Blockages

• Fit a hair catcher strainer over your drain — inexpensive and very effective
• Do a hot water flush weekly
• Clean the drain cover monthly
• Avoid washing large amounts of hair down the drain after brushing

When to Call a Professional

If you've worked through all the steps above and the bath is still draining slowly — or if water is backing up into other fixtures — the blockage is likely deeper in the waste system, possibly in the trap, the branch drain, or the main drain line. At this point, you'll need a licensed plumber.

Drainlaying and work on the main drainage system is restricted work under the Plumbers, Gasfitters and Drainlayers Board (PGDB) regulations, meaning it must be carried out by a licensed tradesperson. Attempting to dismantle traps or underground drainage yourself without the right knowledge can cause leaks, damage, or compliance issues under the NZ Building Code.

You can find a qualified local plumber on tradedirectory.co.nz to get the job sorted quickly and correctly.

Sources & Further Reading

• Plumbers, Gasfitters and Drainlayers Board – Licensed Work
• MBIE Building Performance – NZ Building Code
• WorkSafe NZ – Safe Use of Chemicals at Home
• BRANZ – Home Maintenance Guidance
• Bunnings – Drain Cleaning Tools
• Mitre 10 – Plumbing & Drainage