A hairline crack in the tank, a chip out of the bowl rim, a lid that didn't survive the trip to the floor — none of these automatically means you're buying a whole new toilet. If yours is a two-piece model, the tank and bowl are separate pieces of porcelain that happened to be sold as a set, and most major manufacturers — TOTO and American Standard especially — sell each half on its own. Order the correct matching piece and you're back in business without disturbing the seal at the floor, at least when it's the tank that failed.
First, confirm the job can be split
This only works on two-piece toilets, where a bolted-on tank sits on top of a separate bowl. On a one-piece toilet, the tank and bowl are a single moulded piece of china, so a crack anywhere means replacing the fixture. If you're not certain which you own — or the damage has you rethinking the design entirely — our one-piece vs. two-piece comparison walks through the trade-offs. Wall-hung toilets are a different case again: the bowl and the in-wall tank are separate components by design, and a damaged bowl can usually be swapped without opening the wall.
Step 1: Find your model numbers
Porcelain doesn't wear a data plate, but the numbers are there if you know where to look. Check these three spots:
- Under the tank lid. Flip the lid over — many brands stamp or ink the model number on the underside, and it's usually the fastest place to find it.
- Inside the tank. Look at the back wall of the tank, above the waterline. A number cast or stamped into the china here identifies the tank itself, sometimes with a manufacture date.
- On the bowl. Check the porcelain behind the seat hinges and under the rim at the back. Bowl stamps are less consistent, but this is where they live when present.
Photograph everything you find, including partial numbers and logos. One important wrinkle: a two-piece toilet usually carries three numbers — one for the combination, one for the tank, and one for the bowl. The number on an old receipt or box is typically the combination number, while the stamp inside the tank is the tank number. When you order, you want the part number for the piece you're replacing, and the manufacturer's spec sheet will confirm which tanks pair with which bowls.
Step 2: Match the exact tank-to-bowl pairing
This is where people go wrong. Tanks and bowls are engineered as pairs: the tank releases a precise volume of water at a rate the bowl's rim channels and trapway were designed around. A tank from a different model may physically bolt on and still flush badly, run long, or leak at the joint. Before ordering, verify:
| What to check | Why it matters |
|---|---|
| Exact compatible pairing | Manufacturers publish which tanks fit which bowls. "Close enough" isn't a category here — match the listed pairing. |
| Flush volume | A bowl designed around a 6-litre flush won't necessarily clear properly with a tank that delivers less, and vice versa. |
| Flush valve and gasket size | Two-piece toilets commonly use 2-inch or 3-inch flush valves, and the tank-to-bowl gasket must match the opening. |
| Colour | Whites vary by brand and era. A current-production tank in the same colour name is usually a close match; porcelain from a different brand rarely is. |
If the manufacturer no longer lists a compatible tank or bowl for your model, treat that as a strong signal to replace the whole toilet rather than gamble on an approximate fit.
Replace the small parts while you're in there
Whichever half you're swapping, budget for fresh hardware — reusing decade-old rubber is how a straightforward repair turns into a slow leak:
- Tank-to-bowl gasket — the sponge or rubber seal between the two pieces. Always new, sized to the flush valve.
- Tank bolts and washers — brass bolts with rubber washers; the corroded originals rarely survive removal anyway.
- Fill valve and flapper — many replacement tanks ship with the internals factory-installed, which is worth confirming on the listing. If yours doesn't, this is the time.
- Wax ring and closet bolts — required if you're replacing the bowl, since it has to come off the floor flange.
- Supply line — cheap insurance while the water is already off.
You'll find gaskets, bolt kits, fill valves, seats, and other repair hardware in our toilet components collection, alongside brand-specific tanks and lids.
When a whole new toilet is the smarter buy
Sometimes the honest answer is that the broken part is an exit ramp, not a problem. Full replacement usually makes more sense when:
- The toilet predates the mid-1990s. Older toilets can use 13 litres or more per flush. Sourcing vintage parts keeps that water bill alive, and matching aged porcelain is difficult regardless.
- It's an early 6-litre model that never flushed well. First-generation 6-litre designs earned their poor reputation. A new tank faithfully preserves a weak flush, whereas a modern toilet with a strong MaP score fixes it — our guide to MaP scores explains the one number worth checking.
- Both pieces are damaged, or the bowl is cracked through. Once you're pricing a tank and a bowl separately, a new combination is usually the better value and comes with a fresh warranty.
- You can't identify the brand. Builder-grade toilets from defunct or unbranded manufacturers often have no parts channel at all.
- You wanted to upgrade anyway. Chair height, skirted sides, dual flush — if any of those are on your list, put the repair money toward them instead.
If you land on replacement, measure your rough-in before you fall for anything — our rough-in measuring guide takes two minutes and prevents the most common ordering mistake. Then browse the full toilet collection or jump straight to two-piece models.
Frequently asked questions
Can I put any tank on my toilet bowl?
No. Tanks and bowls are matched pairs — flush volume, valve size, bolt spacing, and rim wash pattern all have to line up. Stick to the pairings the manufacturer lists for your bowl. An unmatched tank might bolt on, but poor flushing and leaks at the gasket are the usual result.
Where is the model number on a TOTO or American Standard toilet?
Check the underside of the tank lid first, then the back wall inside the tank above the waterline. Both brands typically mark the tank there; bowl markings, when present, sit behind the seat hinges or under the rear rim. Keep in mind the tank and bowl carry different numbers from the combination number the toilet was originally sold under.
Can I replace just the bowl on a one-piece toilet?
No. A one-piece toilet is a single casting, so there's no separable bowl or tank to order — damage to any part of the porcelain means replacing the fixture. It's one of the genuine practical advantages two-piece toilets still hold.
Is replacing just the tank hard to do myself?
It's one of the friendlier DIY plumbing jobs: shut off the water, drain and unbolt the old tank, set the new gasket and bolts, and tighten evenly so the porcelain isn't stressed. No wax ring, no lifting the bowl. Replacing a bowl is more involved, since the fixture has to come off the floor flange and be reset on a new wax ring.