What Size Sewer Pump Station Do I Need?
Written for Australian homeowners, builders and plumbers who've just found out the drain sits below the sewer main.
Nine times out of ten the question arrives in the same shape. Someone's putting a granny flat out the back, or converting a basement, and the plumber has broken the news that gravity isn't going to do them any favours. Now they're on our site at half past nine at night trying to work out whether they need the little one or the big one.
So here's the answer, without the runaround.
The short version
For most Australian homes, a 250L sewer pump station is the right call. It handles a granny flat, a basement bathroom, a laundry, a garbage room, anywhere you've got a handful of fixtures that need lifting up to the main.
You step up to 900L when you're draining a whole house, and 1200L when it's a large home, a small commercial site, or you want a dual-pump setup so there's a backup if one fails.
That's the ninety-percent answer. The rest of this page is the ten percent, the bits that catch people out.
Why tank size is the wrong first question
Everyone asks about litres first. It's the number on the box, so it's the number people fixate on.
But the tank isn't doing the work. The tank is just a holding pit. What matters is whether the pump can shift what you're putting into it, high enough and fast enough to get it where it needs to go.
Get the pump right and an undersized tank is a minor inconvenience. It just cycles more often. Get the pump wrong and it doesn't matter how big the tank is. You've got a very expensive hole in the ground.
Work out what's draining into it first
Sit down and count the fixtures. Toilets, basins, showers, laundry tub, washing machine, kitchen sink, dishwasher. That's your load.
Then ask the question everyone skips: how many of those get used at once? A granny flat with one bathroom and a kitchenette has a peak load of maybe two fixtures running together. A five-bedroom house on a Sunday morning is a completely different animal.
The three sizes, and who actually buys each
250L: the one most people need
Roughly 880mm deep, 720mm across. It fits through a standard doorway, which matters more than you'd think when the install is round the back of an existing house with no side access.
This is the size for:
- Granny flats and secondary dwellings
- Basement bathrooms and below-ground laundries
- Garbage rooms and bin stores
- Low-lying properties where one section sits under the main
- Small commercial, like a shop with a single amenities block
Two options here, and the difference is the pump inside:
The Kwikflo 250L Sewer Pump Station comes pre-assembled with the valves and pipework already fitted. Priced by state, from $3,199.
The REEFE RGM055A 250L Sewer Pump Station runs a compact grinder pump and includes a high-level alarm. $3,349.
There's also the REEFE QubeX 250 Series at $3,499 if you want the heavier-duty grinder.
900L: whole-of-house
1200mm deep, 1075mm across. Bigger hole, bigger excavation, and you'll want machine access to the spot.
You're looking at 900L when the pump station is taking everything the house produces, not just one wing of it. Four bedrooms, two or three bathrooms, the lot. The extra volume buys you buffer. The pump runs less often and lives longer for it.
The Kwikflo 900L Sewer Pump Station is $4,699, available single or dual pump.
1200L: large homes and light commercial
1600mm deep, 1075mm across. That depth is worth noting before you commit, because at 1.6m you're into shoring and confined-space territory on the install, and that changes the labour cost.
Worth it when you're running a large home, a childcare centre, a small commercial kitchen, or anywhere a failure means the site stops. The Kwikflo 1200L Sewer Pump Station is $4,150 single pump.
Quick comparison
| Size | Depth | Diameter | Typical application | From |
|---|---|---|---|---|
| 250L | 880mm | 720mm | Granny flat, basement bathroom, garbage room | $3,199 |
| 900L | 1200mm | 1075mm | Full house, 3 to 4 bedrooms | $4,699 |
| 1200L | 1600mm | 1075mm | Large home, light commercial, dual pump | $4,150 |
Prices are Waternex list prices in AUD including GST, current as of July 2026. The 250L Kwikflo is priced by state.
Browse the full range in Sewer Pump Stations or the wider Packaged Pump Stations collection.
Head height: the number everyone forgets
This is where sizing actually goes wrong, and it's got nothing to do with litres.
Head is how high the pump has to lift the waste. Every pump has a curve: the higher it pushes, the less it moves. Push it past its limit and flow drops to a trickle, or stops.
Measuring it takes five minutes
Two numbers, added together.
Static head. Vertical distance from the bottom of the pit to the highest point of the discharge line. Not to the sewer main, but to the highest point the pipe reaches. If it climbs over a retaining wall before it drops away, that peak is your number.
Friction loss. Pipe fights the flow. Long runs, tight bends and narrow pipe all cost you. A rough field rule is to add about a metre of head for every 10 metres of horizontal pipe run, plus a bit for each bend.
Say the pit is 1.2m deep, the discharge climbs 2m to clear the boundary, and there's 30m of pipe to the main. That's 1.2 + 2 = 3.2m static, plus roughly 3m friction. Call it 6.2m of head, then size the pump above that with margin. Don't buy one rated at exactly 6.2m.
Your plumber should verify this properly with the actual pipe spec. The estimate above gets you in the right aisle, not the right shelf.
Sewer or stormwater? They're different pumps
Same tank. Completely different machine inside. People mix these up constantly and it's an expensive mistake.
A sewer station runs a grinder or cutter pump. It's built to chew through solids: the stuff that goes down a toilet, plus the stuff that shouldn't but does anyway. Wet wipes, mostly.
A stormwater station runs a drainage pump. Higher flow, no cutter, because it's shifting rainwater and runoff. Cheaper, and it will not survive being fed sewage.
If you're pumping rainwater, driveway runoff or basement seepage, you want the stormwater version, either the Kwikflo 250L Stormwater Pump Station at $2,607, or for lighter domestic drainage the REEFE Stormwater Pit & Pump from $799 in 40L, 85L and 180L.
Full range: Stormwater Pit and Pump Systems.
Don't skip the access cover
The lid is rated by what can drive over it, Class A through G. Pedestrian-rated covers are standard on most packages. If that pit ends up under a driveway (and plans change during a build more often than anyone admits), you need a load-rated cover instead.
Cheap to specify at order. Expensive to retrofit once there's concrete over it.
Four mistakes we see over and over
Sizing on tank volume alone. Covered above. The pump does the work.
Forgetting the discharge climbs. People measure to the main and miss the hump in between.
No allowance for access. A 1075mm tank won't go down a 900mm side path. Measure the route in, not just the hole.
Single pump where it should be dual. If a failure means the site stops trading or the house becomes unusable, the second pump isn't a luxury.
Frequently asked questions
What size sewer pump station do I need for a granny flat?
A 250L station covers a standard granny flat: bathroom, kitchenette, laundry. Step up only if you're running unusually long pipe or lifting more than about 6 to 7 metres.
Can one pump station handle both sewer and stormwater?
Technically the tanks are rated for both, but the pump has to suit the dirtier job, meaning a grinder. In practice most councils and plumbers want them kept separate. Ask before you plan on combining them.
How deep does the hole need to be?
Tank depth plus bedding and cover. A 250L at 880mm typically wants a metre-plus of excavation; a 1200L at 1600mm is a considerably bigger job.
Do I need council approval?
Usually yes, and requirements vary by state and by water authority. Your licensed plumber handles this as part of the connection. Don't order until you know what your authority requires.
How long do they last?
The tank outlives everything. The pump is the wear item. Expect years, not decades, and expect it to depend heavily on what goes down the drain.
Still not sure? Ask us before you dig
Send us your fixture count, pit depth and the run to the main, and we'll tell you which unit fits. It takes a minute and it's free, and a lot cheaper than putting the wrong station in the ground.
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This guide is general information for Australian conditions and isn't a substitute for advice from a licensed plumber. Pump station installation and sewer connection are regulated work, and requirements differ between states and water authorities. Have your plumber confirm sizing, approvals and compliance before you order.