How to Replace a Toilet Cistern Inlet Valve
I got called to a house in Ashgrove last month where the toilet had been hissing and refilling every 20 minutes for over a year. The owner had been hearing it every night, getting up to check it, going back to bed. He’d put up with it for 14 months before ringing me. The fix was a $35 WaterMark-certified Caroma inlet valve from Reece, 15 minutes with a shifter. He’d paid me $180 to walk in the door plus the part — total $215. He could have done it himself for $35 if he’d known it was homeowner-legal. I see this go wrong more times than I can count: people put up with leaks they could fix in a quarter-hour because every guide on the internet assumes US “ballcock and flapper” plumbing. Aussie cisterns dont work that way — we use vertical-action inlet valves with bottom-entry or side-entry BSP connections — and the swap is genuinely one of the few cistern jobs the homeowner is allowed to do.
Quick legal note up front. Replacing a toilet cistern inlet valve is one of the few “inside the cistern” jobs that’s homeowner-legal in every Australian state, provided you use a WaterMark-certified valve and don’t modify any pipework on the supply side. You are NOT legally allowed to replace the actual flexi hose feeding the cistern in some states (Section A2.2 of AS/NZS 3500.1 — that’s licensed plumber work in QLD, NSW and VIC), and you cant alter the stop tap. But the valve inside the cistern itself? Yes, that’s homeowner DIY. Cheaper to do once, properly.
What you’ll need
- Adjustable shifter (250 mm — the 150 mm stubby doesnt give enough leverage on a stiff locknut)
- Replacement inlet valve — WaterMark-certified, matching your inlet position (bottom-entry or side-entry) and BSP thread size (almost always 1/2″ BSP)
- Bucket and old towel
- Rubber gloves
- Plumbers tape (PTFE / Teflon) — but only on threads the manufacturer specifies
- Spirit level (optional but useful for getting the float orientation right)
- A torch — cisterns are dark inside
Brand-wise, Caroma, Fluidmaster Pro 400 (Aussie spec) and Geberit are all WaterMark-certified and reliable. Avoid eBay generics that don’t show a WaterMark certificate number on the box — they’re not legal to install, and using one voids your home insurance for water damage if it fails. Reece, Tradelink and Bunnings all stock compliant valves.
Step 1: Identify your cistern type
Take the lid off the cistern and look inside. Two common Aussie configurations. Bottom-entry inlet — water pipe enters from below, vertical inlet valve sits in the centre or side. Most common in homes built since the mid-90s. Side-entry inlet — water pipe enters through the cistern side wall. More common in older Caroma cisterns and commercial installs. Buy the right type — they’re not interchangeable. Taking a photo and showing the Reece bloke will save you a return trip.
Step 2: Turn off the stop tap
The stop tap is the small chrome valve on the wall behind or beside the toilet, where the flexi hose connects to the building plumbing. Turn it clockwise until it stops. If you dont have a stop tap — some older houses don’t — turn off the mains at the meter and add “fit a stop tap” to your next licensed plumber job. Every toilet should have one for exactly this reason.
Step 3: Flush the toilet to empty the cistern
Hold the flush button down to drain as much water as possible. There will still be 100–200 ml left in the bottom of the cistern — that’s what the towel and bucket are for in Step 5. Don’t try to scoop it out with a cup; just be ready for the dribble when you disconnect the hose.
Step 4: Disconnect the flexi hose from the inlet valve
The flexi hose connects to the inlet valve at the bottom (or side) of the cistern with a brass nut. Use the shifter to undo it, anti-clockwise as you look up at it. Have the bucket and towel ready — residual water will dribble out. Don’t yank the flexi hose around — its fine to leave dangling, but if it kinks visibly you may need a new one, and replacing the flexi is licensed work in some states. Check it carefully before reusing.
Step 5: Remove the locknut securing the valve to the cistern
Inside the cistern (or underneath, depending on design), there’s a large plastic locknut that clamps the valve through the porcelain wall. Undo it by hand — they’re usually finger-tight, designed for service. If its seized, gentle shifter use is fine but don’t crank hard or youll crack the porcelain. Once the locknut is off, lift the old valve straight out. Lay it on the towel so you can compare it to the new one before installing.
Step 6: Inspect the rubber washer and the cistern hole
The old valve had a rubber sealing washer between the valve body and the porcelain. Make sure it comes out (sometimes it sticks to the porcelain). Clean the area with a rag — old mineral deposits can prevent the new washer sealing. Check for hairline cracks in the porcelain around the hole; if you see one, stop and call a licensed plumber, because tightening a new valve into a cracked cistern will split it and that’s a whole-cistern replacement.
Step 7: Fit the new valve into the cistern
The new valve comes with a fresh rubber washer (usually pre-fitted). Drop the valve through the hole from above, with the washer between the valve body and the porcelain. Hand-tighten the locknut from below. Don’t use the shifter on the locknut — these are designed to be hand-tightened only, and over-torquing cracks the porcelain. Heres where most people go wrong — they grab the shifter out of habit. Hand-tight only. Firm finger pressure is what the manufacturer engineered for.
Step 8: Reconnect the flexi hose
The flexi hose nut goes onto the threaded shank of the new valve. Most Aussie inlet valves have a built-in fibre or rubber washer in the nut — DO NOT add Teflon tape to this thread unless the manufacturer specifies it (check the instructions in the box). Adding tape where its not needed prevents the washer seating and causes leaks. Hand-tight, then a quarter-turn with the shifter is enough. The missus had to remind me of this on her parents’ loo when I went to “just give it a bit more” — quarter turn means quarter turn.
Step 9: Set the water level
Most modern Aussie inlet valves have a height-adjustable float — turn the screw on top of the valve or slide the float collar up or down. The waterline target is usually marked inside the cistern as a moulded line on the porcelain (or a printed “WL” mark). Setting it too high causes the overflow to trickle constantly down into the bowl, wasting water; setting it too low gives a weak flush. Adjust until the water sits 10–15 mm below the top of the overflow tube. For related cistern internals see our replace toilet seat guide — different part, same general approach to porcelain-friendly torque.
Step 10: Turn on the stop tap and test
Open the stop tap slowly. If you hear hissing or see drips at the flexi connection, close the tap and re-tighten the nut a quarter turn. Once it’s filling cleanly, watch the cistern fill to the line and shut off. Flush three times in a row to confirm. Run a dry tissue around every joint and under the cistern — any moisture means a leak you need to chase before you call it done. Five minutes of testing now is better than discovering a slow weep at 3am when the carpet’s already wet.
When to call a tradie
Heres where the legal line sits. Inlet valve swap — homeowner DIY in every state, provided the valve is WaterMark-certified. NOT homeowner DIY: replacing the flexi hose (licensed in QLD, NSW, VIC under AS/NZS 3500.1 Section A2.2), replacing the stop tap, replacing or moving the supply line, replacing the entire cistern, or any work where the cistern is removed from the pan (that disturbs the doughnut washer, which is licensed). If the porcelain is cracked, if the cistern is wobbling on its mount, if the flush valve (outlet, not inlet) is the actual problem — stop and ring me. WaterMark certification is what keeps your home insurance valid; generic eBay valves are not legally installable and a denied claim is genuinely brutal. For a related licensed-DIY job, see our replace mixer tap cartridge guide.
Common screw-ups
- Non-WaterMark valve. Voids insurance, illegal to install. Buy from Reece, Tradelink or Bunnings only.
- Shifter on the locknut. Cracks the porcelain. Hand-tight only.
- Teflon tape where it isn’t specified. Stops the inbuilt washer seating, causes leaks.
- Float set too high. Constant overflow trickle, wasted water on the rates bill.
- Phantom flushes after the swap. That’s not the inlet — its the outlet flush valve leaking past the seal. Different part, occured to me twice on jobs where the homeowner had already replaced the inlet.
Cost & time
$30–$45 for a Caroma or Fluidmaster Pro 400 WaterMark-certified valve from Reece or Bunnings. Time: 15–20 minutes for a confident first-timer, 30 minutes if it’s your first toilet job. Save at least $150 over a plumber callout. Worth doing yourself.
The Tomo rule — wrap
Use a WaterMark-certified valve, full stop. The cert number is printed on the box and listed on the WaterMark register at abcb.gov.au. Generic eBay valves are not legally installable, and your home insurance will deny a water damage claim caused by a non-compliant fitting — I’ve seen the rejection letters. The actual installation is genuinely 15 minutes once you’ve got the right part. Hand-tight locknuts, quarter turn on the flexi nut, no Teflon unless specified, and the float set 10–15 mm below the overflow rim. Got a toilet that’s still leaking after a valve swap, or a cistern that’s actually cracked? Send us a write-up and well point you to the right fix.
