Why Does My Sink Not Have a U-Bend? Understanding Plumbing Traps in Australian Homes

If you’ve looked under your kitchen or bathroom sink and noticed there’s no U-bend (trap), you’re right to wonder if that’s normal — or even legal.

In Australia, all household fixtures that connect to the sewer — like sinks, basins, and showers — must have a water trap installed under the Plumbing Code of Australia (AS/NZS 3500). This small, curved section of pipe keeps dangerous sewer gases out of your home.

Let’s unpack what a U-bend does, why it might be missing, and what you should do if your sink doesn’t have one.

What Is a U-Bend or P-Trap?

A U-bend, S-trap, or P-trap is a curved section of pipe that always holds a small amount of water. That water forms a seal that blocks sewer gases while still allowing wastewater to flow away.

Common types used in Australian homes:

• P-Trap – common under wall-mounted basins and kitchen sinks.

• S-Trap – used where the pipe exits through the floor (common in older homes).

• Bottle Trap – often seen on modern vanities for a cleaner look but works the same way.

Without one, you’ll likely notice a bad smell — a clear sign something’s wrong.

Is It Legal to Have No U-Bend in Australia?

❌ No.

Under AS/NZS 3500.2:2021 – Sanitary Plumbing & Drainage, every fixture connected to a sanitary drain must have a water trap with at least a 50 mm water seal.

A sink or basin with no visible U-bend is non-compliant unless the trap is built into another approved component (for example, an appliance trap or combined fixture unit).

Why Might My Sink Not Have a U-Bend?

Here are the most common reasons:

1. It’s hidden or integrated

Modern sinks sometimes have the trap concealed behind cabinetry or built into the waste assembly.

2. Renovation shortcut

In DIY or unlicensed renovations, traps are sometimes removed or installed incorrectly to make space for drawers or appliances. This breaches the plumbing code.

3. Poor installation or damage

A previous leak or vanity refit might have left the trap missing or misaligned — even a small gap can break the water seal.

What Happens If There’s No U-Bend?

Without a working trap, you may experience:

• Sewer gas odours coming from the drain

• Mould or bacteria growth

• Insect infestations (flies and gnats)

• Health hazards from sewer gas

• Potential code or inspection issues

A missing or dry trap isn’t just unpleasant — it’s a health and compliance risk.

How to Fix a Sink Without a U-Bend

1. Check if the trap is hidden behind cabinetry or inside the vanity.

2. Call a licensed plumber to confirm compliance.

3. If missing, the plumber can:

   
   

   • Install a P-trap or bottle trap.

   • Correct misaligned pipework.

   • Ensure the trap is vented properly.

🧰 Plumb Melbourne can retrofit compliant traps to meet Australian Standards and eliminate odours fast.

What About Apartments or Commercial Premises?

Some modern buildings use common trap systems (like floor traps or trap-primers). These are legal only when approved by a certifier and installed by licensed plumbers during construction.

If you manage multiple units, it’s worth booking a compliance check to ensure every sink meets code and tenant safety requirements.

When to Call a Plumber

You should contact a licensed plumber if you notice:

• Persistent odours near the sink

• Slow drainage or gurgling noises

• No visible U-bend under the basin

• Recent DIY renovations or vanity replacements

📞 Call Plumb Melbourne on 0437 296 544 for inspections across South-Eastern and Northern Melbourne, including Glen Iris, Doncaster, Preston, and Camberwell.

Every sink and basin in Australia must have a properly installed U-bend or trap — it’s not optional. This small component protects your health, stops bad smells, and keeps your property compliant with the Plumbing Code of Australia.

If your sink doesn’t have one, or you’re unsure whether it meets the standards, it’s time for a professional inspection.

🛠️ Plumb Melbourne specialises in residential and property-management plumbing that meets every code and safety requirement — from blocked drains to compliance audits.

👉 Book a Compliance Inspection or call 0437 296 544 today.