How to Replace a Toilet Seat

By Tomo — licensed plumber, Brisbane.

Here’s a fun bit of trivia from the regulator: replacing a toilet seat is one of the only “plumbing” jobs that’s legal homeowner DIY in every Australian state and territory. No license, no certificate of compliance, no notifiable work form. You’re not touching the cistern, you’re not touching the inlet, you’re swapping a piece of moulded plastic that bolts to the porcelain. The Plumbing Code of Australia doesn’t even consider it plumbing work.

And yet, of all the jobs I get called out to “fix” because someone has had a crack themselves, toilet seats are top three. Not because the job is hard — it isn’t — but because Aussie toilets aren’t a single shape. Caroma, Fowler and Stylus between them sell about a dozen pan profiles, and a “universal” seat from Bunnings only fits one of them. The other 80% of first-timers come home with a $39 seat, get it on the bowl, and discover the bracket sits 20 mm proud of the porcelain or the lid clouts the cistern when it lifts.

This guide will get it right the first time. Take a photo of your bowl before you go to the shop. I’ll show you what to photograph and why.

What you’ll need

• A new toilet seat (matched to your pan — see Step 1)
• An adjustable spanner or 13 mm socket
• Long-nose pliers
• A rag and some white vinegar
• Methylated spirits and a microfibre cloth
• A torch
• Optional: a hacksaw blade (for seized brass bolts on older bowls)

Step 1: Identify your pan shape and brand before you buy

This is the step that catches everyone. Aussie pans come in three broad shapes — D-shape (most common, rounded front, flat back), square (Caroma Cube, Stylus Symphony, Fowler Aspire), and round (older 1980s–90s suite). The seat hinge geometry differs across all three, and within “D-shape” the bolt-hole spacing varies by brand.

Bunnings universal seats (Mondella, Estilo, Kado-branded) only fit standard D-shapes. If you have a Caroma Cube, a Stylus Symphony, a Caroma Liano, or a Fowler Newport, you need a brand-specific seat from Reece, Tradelink or directly from Caroma. A genuine Caroma Cube seat is around $145; a knockoff that “looks the same” will sit 8 mm proud at the back and rattle every time you sit on it.

Take a photo of: (1) the pan from above, (2) the cistern label or any model name moulded into the porcelain at the back, (3) the existing bolt hole spacing measured centre-to-centre. Send those to the Reece bloke and he’ll match it.

Step 2: Work out top-fix vs bottom-fix

Lift your existing seat lid and look at where the seat hinge bolts to the bowl. If you see two bolt heads on top of the porcelain (usually plastic caps), and underneath the bowl rim there’s no nut visible — that’s a top-fix. The bracket has expanding plugs that grip blind holes in the porcelain.

If you see a threaded brass shaft passing right through the porcelain with a wing nut or hex nut underneath — that’s a bottom-fix. Most pans made in the last 15 years are top-fix because it’s quicker on the production line. Older Caroma Caravelle, Fowler suites, and almost everything pre-2005 is bottom-fix. Buying the wrong type means the bolts physically won’t engage, no matter how much you swear at them.

Step 3: Remove the old seat — bottom-fix

Reach behind the bowl with one hand and feel for the wing nut or hex nut on the underside of the porcelain. With your other hand, hold the bolt head on top steady (it’ll be slotted for a flathead screwdriver, or have a plastic cap you’ll need to lever off first). Undo the nut anti-clockwise. If it’s seized — and on anything older than 10 years it usually is — soak it in white vinegar for 20 minutes, then try again. Brass nuts on stainless bolts go green and lock up something shocking.

If the nut won’t shift even after vinegar, wedge a hacksaw blade (no frame) between the nut and the porcelain and saw through the bolt. Don’t go at it with a full hacksaw — you’ll crack the bowl, and a cracked Caroma is a $400 problem.

Step 4: Remove the old seat — top-fix

Most modern top-fix seats have a quick-release button or slider on the hinge. Press it and lift the whole seat up and off. With the seat removed, you’ll see two plastic plugs in the porcelain. Some are unscrewed with a flathead, some pop out with a sharp upward pull, and Caroma’s are a quarter-turn lever. If you can’t tell, look up your model on the Caroma support site — they have diagrams for every pan they’ve made since 1995.

Step 5: Clean the porcelain properly

This is the step Jen would be proud of — prep matters. With the old seat off, you’ll see two crescents of grime where the rubber bumpers sat. Hit it with white vinegar, leave for five minutes, then scrub with a microfibre. Finish with metho on a clean cloth so the new bumpers seat on a dry, oil-free surface. Skip this and the new seat will rock within a fortnight.

Step 6: Fit the new brackets

For top-fix, push the expanding plugs down into the porcelain holes until the shoulder is flush. Tighten the centre bolt clockwise — you’ll feel the plug expand and grip. Stop the moment it’s firm. Over-tightening cracks the porcelain around the hole, which is the other way people kill a $400 pan. Snug, not gorilla.

For bottom-fix, drop the bolt through the bracket, through the porcelain, and finger-tighten the wing nut underneath. Don’t go full noise yet — you want movement to align the seat in Step 7.

Step 7: Fit the seat and check the lid clearance

Slot the seat onto the brackets (most modern ones click into place). Now do two checks:

• Lift the lid all the way back. It should stop before it touches the cistern. If it clouts the cistern — and on Caroma close-coupled suites this is the #1 install fault — your brackets are too far forward. Loosen, slide back 5–10 mm, retighten.
• Sit the lid down and eyeball the gap between the seat and the bowl rim at the front. Should be even left-to-right. If it’s skewed, the brackets aren’t square.

Step 8: Final tighten and bumper check

Once the seat sits true and the lid clears the cistern, tighten everything down. For top-fix, that’s the centre bolt on each bracket. For bottom-fix, hold the bolt head on top with a flathead and tighten the nut underneath with the spanner. Firm, not heroic. Caroma’s official spec is 4 Nm — about the torque you can apply with a stubby spanner using two fingers.

Now look at the four rubber bumpers on the underside of the seat. All four must contact the porcelain when the seat is down. Press each corner of the seat in turn — if any corner rocks, that bumper isn’t seating. Most quality seats have screw-adjustable bumpers; turn them out a half-turn until contact is solid.

Step 9: Test the soft-close (if fitted)

Modern seats almost all have soft-close hinges. Lift the lid to vertical and let go. It should descend slowly and silently, taking 4–7 seconds to close. If it slams, the dampers are dud or the lid is on backwards (yes, this happens). If it sticks halfway, the hinge needs a drop of silicone — never WD-40, which kills the damper grease.

Step 10: Clean up and check again in a week

Wipe the bowl down, pop the bolt caps on (top-fix only), and walk away. Come back in a week and re-check the bracket tightness — porcelain and plastic settle, and a quarter-turn nip-up at day seven stops the wobble that develops in month two.

The Tomo rule

Photograph the pan before you go to the shop, and ask the Reece bloke to match it — don’t trust the box. Bunnings universal seats fit standard D-shape Caromas and not much else. If you’ve got a Cube, a Symphony, a Liano or anything square, factor $120–$150 for a genuine seat and don’t try to save $80 with a knockoff. The knockoff will rock, the brackets will fatigue, and you’ll be doing the job again in eight months. Snug the bolts, never gorilla them — cracked porcelain is a whole-pan replacement, which is a licensed plumber job and a whole different price bracket.

Got a tricky pan or a Caroma model that fights you? Send us a write-up.