Which Basin Waste Do You Need? 32mm vs 40mm, Overflow vs No Overflow

You have chosen the basin, sorted the tapware and found a vanity you love. Then the installer asks which waste you ordered. It is a small fitting, but buying the wrong one can leave the whole vanity waiting.

The confusing part is the terminology. A product might say 32mm, 40mm, universal, overflow or non-overflow, sometimes with several of those descriptions together. Each tells you something different about how it fits.

This Blue Leaf Bathware & Tiles guide explains how to choose a basin waste in Australia, with real product examples and a checklist you can use before ordering.

Quick comparison: what the descriptions mean

32mm vs 40mm basin waste: which size should you buy?

Start with the basin manufacturer's stated waste requirement. If it specifies 32mm or 40mm, use that information to shortlist compatible products, then check each waste's technical details.

Those numbers are not reliable measurements for the visible plug cap or a benchtop cut-out. The cap, fitting body, threaded connection and required opening can have different dimensions. Measuring only the shiny disc in an existing basin will not identify the replacement you need.

Why a 40mm product can suit a basin specifying 32mm

Phoenix describes its 40mm Flat Pop Up Universal Waste as suitable for basins specifying a 32mm waste, while connecting to 40mm pipework. That is a useful example of basin compatibility and outlet connection being described separately.

It does not mean every 40mm waste fits every 32mm basin. Read the manufacturer's compatibility statement for the exact model rather than making the decision from the product title.

Overflow vs no overflow: match the basin's design

An overflow is an additional opening in the basin, often near the rim, with a drainage path leading towards the waste. When water reaches that opening, it has another route out while the main plug is closed.

A compatible overflow waste accommodates that path. You may see it described as slotted or with overflow. A non-overflow waste, sometimes called unslotted, is intended for a basin without that arrangement. Universal models may provide both configurations.

Check the basin specification rather than relying on its shape. Above-counter does not automatically mean no overflow. If you are still selecting the basin itself, our bathroom basin buying guide explains the different installation styles.

An overflow is an additional drainage route, not a guarantee against overfilling. Keep an eye on a filling basin, especially where there is no overflow.

Are universal basin wastes actually universal?

Universal usually describes a particular combination of features. A model might support both overflow and non-overflow use, offer 32mm and 40mm connections, or do both. The instructions tell you which.

For example, the Fienza Universal Pop-Up / Pull-Out Basin Waste, model WAS72BN, supports overflow and non-overflow configurations. Fienza also states that its 40mm outlet configuration uses the supplied adaptor.

That makes it flexible, but the required configuration still needs to be set correctly. It is also specified for basins only. Do not assume the word universal extends its use to a bath or kitchen sink.

Some basins nominate particular compatible waste models. Check those restrictions before choosing another fitting with a similar description.

The fit checks that matter before ordering

1. Basin model and waste requirement

Find the exact basin name, model number and current specification sheet. Record its waste requirement and whether the waste is included. Two bowls that look similar can need different fittings.

If the waste comes with the basin, check whether its finish suits your plans before buying a second one. A matching-looking replacement still needs to meet the original compatibility requirements.

2. Drain opening and sealing surfaces

The fitting must suit the basin's opening and the surfaces where its seals sit. Ask your plumber to compare the basin drawing with the waste drawing, including the flange and body dimensions. Avoid ordering from a rough measurement taken across an installed plug.

3. Installation thickness and fitting length

Check the thickness the fitting must clamp through and its permitted installation range. The relevant measurement depends on the basin and mounting arrangement; it is not always the entire benchtop thickness.

A fitting that is too short may not secure properly. A longer fitting can also affect space beneath the basin, so check the full assembly rather than choosing extra length just in case.

4. Space under the vanity

Allow room for the waste body, trap, connections and maintenance access. Drawer backs or internal shelves can conflict with the assembly. If you are changing the cabinetry, use our bathroom vanity dimensions guide alongside the product drawings.

Three examples that make the choice clearer

Example 1: an above-counter basin with an overflow

The Fienza Willow Above Counter Basin specifies a 32mm waste with overflow. Its countertop position does not change that requirement. Shortlist a waste approved for that specification, then confirm the connection and physical fit.

Example 2: a bowl with no overflow

Suppose your selected basin specifies a 32mm non-overflow waste. Choose a suitable non-overflow fitting or a universal model approved for that basin and configured accordingly. Do not buy an overflow-only fitting because its colour matches your tap.

Example 3: retaining the existing plumbing

You are replacing the basin but keeping the vanity and drainage position. Check the new basin's requirement and the existing trap connection separately. A compatible waste or adaptor may help, but it cannot compensate for an unsuitable opening, insufficient fitting length or an obstructed overflow path.

A basin waste and a bottle trap do different jobs

The waste sits in the basin opening. The trap is beneath it and retains a water seal that helps stop drainage odours entering the room. Buying one does not necessarily include the other.

When comparing bottle traps and basin trap options, check connection compatibility, outlet position and the available space. Your plumber should assess the assembly as a whole.

For a wall-hung basin with exposed plumbing, the trap's finish matters visually. Inside a vanity, drawer clearance and access may be more important. Either way, matching finishes alone do not establish a workable connection.

Replacing a waste in an older basin

Keep the basin's identity separate from the old fitting's identity. Photograph the basin, visible waste and accessible plumbing, and look for product markings or an original invoice. Ask your plumber which measurements are needed before ordering a replacement.

For several bathrooms, make a separate basin-and-waste list for each room. A family bathroom and ensuite may use different overflow arrangements even when their fittings look alike. Confirm each pairing before placing a combined order.

Pop-up, pull-out or traditional plug?

A pop-up waste opens and closes through its plug mechanism. Some current models also have a removable top section, making routine cleaning easier. A traditional plug-and-waste uses a separate plug. Choose the operation you prefer after confirming compatibility.

For a frequently used family basin, think about cleaning access and replacement parts. A neat cap is appealing, but being able to remove accumulated hair and residue matters after the bathroom is finished.

Match the finish after you have confirmed the fit

Brushed brass, brushed nickel, gunmetal and matte black can look different across brands. Compare finish names and samples where available rather than assuming two products will match because both say brushed.

A coordinated waste is worth planning with the mixer and any exposed trap. Our bathroom tapware buying guide can help with the broader selection.

Choosing a new mixer as well? Use our separate basin tap height and spout reach guide when checking that pairing.

Slow drainage: check the cause before changing waste size

Before replacing a 32mm waste with a product labelled 40mm, have the cause checked. Build-up, the plug mechanism, the trap or downstream pipework may need attention. A larger number on the box does not guarantee better drainage.

If you are replacing a sticking plug, ask whether a compatible mechanism is available first. Replacing the entire waste may be unnecessary when the existing body is suitable and a matching service part is available.

For routine cleaning, follow the fitting's care instructions. Remove a plug assembly only as the manufacturer allows, and use cleaning products suitable for its finish. An easy-clean design is useful, but it does not mean the whole waste should be dismantled casually.

Australian installation and product checks

Use a licensed plumber for the waste and trap installation. In NSW, plumbing work requires the appropriate licence or certificate regardless of the job's cost. For a Sydney bathroom replacement, ask the plumber to confirm compatibility before you place the order.

WaterMark is another relevant check. The ABCB's schedule notes that basin waste outlets require certification. Confirm the exact product's certification using its model or certificate details; a familiar brand name alone is not the check.

Your basin waste ordering checklist

• Basin: exact model and current waste specification.
• Overflow: present, absent or a specific connection arrangement.
• Fit: opening, sealing surfaces and permitted installation thickness.
• Connection: waste outlet, trap and any approved adaptor.
• Clearance: drawers, shelves and maintenance access.
• Inclusions: waste, adaptors and other supplied components.
• Finish and care: colour, cleaning access and product instructions.

Frequently asked questions

How do I know whether I need a 32mm or 40mm basin waste?

Check the basin's specification first, then the waste's stated compatibility and outlet connection. The product title alone may not distinguish basin fit from pipework size.

Can a 40mm waste fit a basin that specifies 32mm?

Some products are designed for that combination. Phoenix's Flat Pop Up Universal Waste is one example. Treat this as model-specific compatibility, not a rule for all wastes.

Do above-counter basins always need a non-overflow waste?

No. Above-counter describes how the basin is mounted. Check whether that particular basin has an overflow and which waste its manufacturer specifies.

Can I use a universal waste on a basin without an overflow?

Yes, if the model supports non-overflow use and suits the basin. Follow its instructions for configuration; some universal fittings need an adjustment or adaptor.

Can I replace just the pop-up cap?

Sometimes, if a compatible replacement is available. Identify the original waste model and mechanism first. A similar cap diameter does not confirm matching threads or operation.

Is the basin waste included with a new basin?

It depends on the product. Check the inclusions before ordering. Also check whether a trap is supplied; a basin, waste and trap can be separate purchases.

Find the right basin waste at Blue Leaf

Keep your basin model number and specification sheet handy while browsing Blue Leaf's basin waste range. If you are choosing the bowl too, compare our bathroom basins and confirm their waste requirements together. Getting these small details right helps your installer arrive with a combination that actually fits.

References and product resources

• Phoenix: 40mm Flat Pop Up Universal Waste specifications
• Fienza: WAS72BN universal basin waste specifications
• Fienza: Willow basin waste and overflow requirements
• ABCB WaterMark: schedule and waste outlet certification notes
• ABCB WaterMark: product certification search
• NSW Government: plumbing licensing requirements