Toilet Traps Australia | S-Trap vs P-Trap vs Skew Trap
Toilet Traps Australia | S-Trap vs P-Trap vs Skew Trap
What Is a Toilet Trap?
A toilet trap is a curved pipe section at the base of your toilet—critical for keeping your bathroom safe and hygienic. It has two key jobs:
- Water Seal: Holds a small pool of water in its curve to block toxic sewage gases (like methane) from entering your home.
- Waste Drainage: Directs used water from the toilet into your home’s main drainage system.
Australian Standard: All toilet traps must meet AS/NZS 3500.2:2022, which requires a minimum 50mm water seal depth and specific pipe diameters.
S-Trap vs P-Trap vs Skew Trap
Choose the right trap for your Australian home (old, new, apartment, or standalone).
1. S-Trap: The Vertical Drain Classic
Named for its S-shaped curve, this trap connects directly to a vertical drain pipe in your floor. Wastewater flows straight down from the toilet into the under-floor drainage system, making it a traditional choice for many Australian properties.
Ideal For Australian Homes
- Older standalone houses (built pre-2000s)
- Regional properties with under-floor drainage systems
- Floor-mounted toilets in homes with existing vertical soil stacks
Australian Compliance Rules
- Must retain a minimum 50mm water seal (per AS/NZS 3500.2) to prevent gas leaks
- Vertical distance between toilet outlet and trap water seal ≤ 400mm (avoids siphoning)
- Requires a separate vent pipe in multi-story homes to maintain water seal pressure
2. P-Trap: The Wall-Mounted Favorite
With a distinct P-shaped curve, this trap connects to a horizontal drain pipe in your wall (not the floor). The toilet remains floor-mounted, but wastewater flows sideways into the wall before joining the main drainage system—making it a space-saving option for modern homes.
Ideal For Australian Homes
- City apartments and units (Sydney, Melbourne, Brisbane)
- New builds with wall-hung or back-to-wall toilets
- Small bathrooms where under-floor space is limited
- Guest toilets (lower siphoning risk for infrequent use)
Australian Compliance Rules
- Horizontal drain pipe diameter ≥ 100mm (residential use, per AS/NZS 3500.2)
- Pipe must have a 1:40 slope (1mm drop per 40mm length) for smooth drainage
- No additional vent pipe required in most single-story homes (due to horizontal design)
3. Skew Trap: The Angle Solution for Tight Spots
A hybrid design with a slanted (typically 45° or 90°) curve, the skew trap connects to either floor or wall drains at an angle. It’s designed to solve alignment issues where standard S-traps or P-traps can’t fit—making it a go-to for renovations and constrained spaces.
Ideal For Australian Homes
- Bathroom renovations (misaligned old and new drain positions)
- Granny flats, studios, or small auxiliary dwellings
- Heritage homes (avoids rerouting entire drainage systems)
- Homes where toilet placement is limited by structural constraints
Australian Compliance Rules
- Angles limited to 45° or 90° (sharper angles cause clogs, per AS/NZS 3500.2)
- Requires a non-return valve in multi-unit blocks to prevent backflow
- Must be installed by a licensed plumber (DIY installs often fail compliance)
- Retains minimum 50mm water seal (same as S/P-traps)
| Feature | S-Trap | P-Trap | Skew Trap |
|---|---|---|---|
| Drain Type | Vertical (Floor) | Horizontal (Wall) | Angled (Floor/Wall) |
| Best For | Older standalone homes | Modern apartments/new builds | Renovations/tight spaces |
| Compliance Focus | Seal depth + vent pipe | Pipe slope + diameter | Angle + non-return valve |
| Maintenance Difficulty | Hard (under floor access) | Easy (wall panel access) | Moderate (angle-specific parts) |
| Siphoning Risk | Medium (vertical design) | Low (horizontal flow) | Medium (depends on angle) |
Key Concepts for Toilet Selection & Installation
Toilet Set-Out and Mini Lock connectors: solve alignment issues in Australian homes (new builds & renovations).
1. Toilet Set-Out: The Critical Dimension
Definition: The horizontal distance from the finished wall (tile or plastered surface) to the centre of the toilet waste outlet (floor or wall flange). It’s non-negotiable for compatibility—get it wrong, and the toilet pan won’t line up with the waste pipe.
Australian Context
New builds and renovations in Australia mix floor outlets (S-trap) and wall outlets (P-trap), depending on home age:
- Older homes often have non-standard set-outs (due to outdated plumbing practices).
- Renovations cause most issues—installers avoid moving existing wastes to cut costs and comply with local plumbing codes.
Common Australian Set-Out Sizes (mm)
- Compact installs: 90mm (rare, mostly for small ensuite toilets)
- Most common: 140mm, 160mm, 180mm (standard for new builds)
- Larger/offset: 250mm, 270mm (common in older homes or if waste was previously moved)
Pro Tip: Never rely on “typical” sizes. Measure from the finished wall (not bare studs) to the flange centre, to the nearest millimetre—tile thickness alone can add 10–20mm of error.
Simplified Installation Steps
- Remove old toilet, clean the area, and confirm the finished wall line (tile/plaster).
- Measure set-out and confirm flange type (floor = S-trap; wall = P-trap).
- Choose a toilet with a manufacturer-set-out that matches or is slightly smaller than your measurement (small offsets may be adjustable).
- For floor flanges: Ensure flange is level and at the correct height (use a wax ring or rubber gasket rated for your floor finish).
- Fix small mismatches with an approved adjustable connector (see Mini Lock section). For gaps >40mm, call a licensed plumber—moving waste needs compliance with AS/NZS 3500.2.
- Fit pan bolts, seat the pan on the gasket, and tighten bolts evenly (avoid over-tightening—ceramic cracks easily).
- Connect cistern/water inlet, test for leaks, then silicone the base only where the manufacturer recommends (usually a rear bead, not full perimeter—lets you remove the pan later).
Caution: Damaged or corroded flanges must be replaced—they’re the main cause of leaks or rattling toilets. Most Australian councils require a licensed plumber for flange replacement or waste rerouting.
2. Mini Lock: Fix Small Set-Out Mismatches
Definition: A Mini Lock (or adjustable toilet connector) is a certified plumbing accessory that lets you shift the toilet’s waste connection by 10–40mm horizontally. It’s designed to align pans with existing wastes—avoiding costly pipe rerouting in renovations.
Australian Context
Mini Locks are a staple in Australian renovations for two key reasons:
- Renovators often want modern toilets but don’t want to move old wastes (saves time and money).
- They’re ideal for narrow bathrooms or finished tile walls—no need to break tiles to adjust pipes.
Common Adjustment Ranges
- Standard: ±10–20mm (fits most minor mismatches)
- Wide-range: 20–40mm total travel (for slightly larger gaps)
- Specialty: Up to 60–80mm (rare, may impact flush performance—use only if certified for AS/NZS 3500.2)
Compliance Note: Always choose Mini Locks with Australian watermarks or AS/NZS certifications—cheap non-certified models risk leaks and fail council inspections.
Installation Steps
- Confirm the connector matches your flange type (floor = S-trap; wall = P-trap—never mix types).
- Dry-fit the connector first: Place it between the toilet pan and flange to check alignment (ensure pan bolts line up too).
- Clean all surfaces (flange, connector, pan outlet) to remove dirt or old sealant—debris causes leaks.
- If the connector uses rubber gaskets, apply a small amount of soapy water (lubricates for a tight seal—don’t use silicone here).
- Tighten clamps or locking nuts progressively, keeping the pan square to the wall—avoid over-tightening plastic parts.
- Test for leaks: Fill the cistern and flush 3–4 times, checking for water around the connector base. If leaks occur, loosen and realign (don’t just tighten more).
- Trim excess pipe or attach cover shrouds (if included) to hide the connector.
Limitations: Mini Locks aren’t for large gaps (>40mm). Excessive offset reduces trap efficiency, causing clogs or sewage smells. For big mismatches, call a plumber to move the waste.
Quick Decision Guide (Australian Homes)
| Scenario | Solution | Compliance Note |
|---|---|---|
| Measured set-out matches toilet spec | Install toilet normally (use correct gasket) | No plumber needed if DIY-compatible (check manufacturer) |
| Mismatch = 10–40mm | Use certified Mini Lock / adjustable connector | Ensure connector has AS/NZS watermark |
| Mismatch >40mm or damaged flange | Call licensed plumber to reroute waste | Waste rerouting requires council approval in most states |
| Heritage home or apartment block | Plumber inspection first (may have strict rules) | Apartments often require strata approval for plumbing changes |
Frequently Asked Questions
Can I measure set-out before tiles are installed?
No—always measure to the finished wall (tile or plaster). If tiles aren’t up yet, add the tile thickness (usually 10–15mm) to your stud-to-flange measurement. For example: Stud-to-flange = 150mm + 10mm tiles = 160mm set-out.
Why do plumbers avoid moving wastes in renovations?
Moving a waste requires breaking floors/walls, rerouting pipes, and re-complying with AS/NZS 3500.2—costing $500–$1,500+. A Mini Lock ($20–$50) is far cheaper and faster, with no structural damage.
My toilet rocks after installation—did I mess up the set-out?
Rocking usually means the flange is uneven or the pan bolts are over-tightened (not set-out). Use a spirit level to check the flange—if it’s uneven, add a shim under the pan (never use silicone to fill gaps). If bolts are tight, loosen them slightly (ceramic cracks easily).
Do I need a plumber for Mini Lock installation?
If you’re comfortable with basic DIY (removing/resetting a toilet), you can install a Mini Lock. But if you’re unsure about alignment or leak testing, hire a plumber—especially in apartments (strata often requires professional installs for compliance).
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