Sewer Pump Stations for Granny Flats
A granny flat sewer pump station is a sealed poly tank with a grinder pump inside it, buried near the flat, that collects the wastewater and lifts it to the sewer main when the drain sits too low for gravity. For almost every granny flat in Australia the right unit is a 250L packaged station with a single grinder pump, and the equipment lands between $3,199 and $3,399. Prices current as of August 2026.
Want your exact size? Our pump station size calculator works out the tank, pump head and flow from who the station serves and how high and far it pumps, then shows the stations that fit.
The call usually comes after the plumber has been out. The slab is pegged, the design is done, and someone has just worked out that the new bathroom sits half a metre below the connection point out the front.
When a granny flat needs a pump station
A granny flat needs a sewer pump station whenever the invert level of its drain sits below the invert of the sewer connection point, which happens on sloping blocks, on low rear yards, and any time the flat goes in behind a house that already took the high ground. Gravity drainage needs fall the whole way. No fall, no flow.
The test is one measurement, not a guess
Your plumber shoots a level from the sewer junction to the proposed drain outlet and compares the two. If the outlet is higher by enough to hold the standard grade the whole run, you drain by gravity. If it is lower, or level, or short by 50mm over 25 metres, you pump. There is no third option.
Common granny flat situations that end in a pump
Rear yards that fall away from the street cause most of the pump station jobs we quote. The house sits high at the front, the block drops to the back fence, and the new dwelling goes where the ground is lowest.
- Sloping blocks where the flat is at the low end
- Conversions of a below ground rumpus or basement into a self contained flat
- Long rear runs where the fall gets used up before the pipe reaches the boundary
What size pump station a granny flat needs
A 250L station is the correct size for a standard granny flat, meaning one bathroom, a kitchenette and a laundry. The fixture load is small and the peak load is smaller again. Volume is not the constraint on this job. Lift is.
The 250L tank is roughly 880mm deep and 720mm across. That matters twice on a granny flat build: the excavation is small enough for a mini excavator, and the tank fits down a standard side path, often the only way in on an established block.
| Dwelling | Typical fixtures | Station size | Equipment from |
|---|---|---|---|
| Studio or one bedroom granny flat | Toilet, shower, basin, kitchen sink, laundry tub | 250L single pump | $3,199 |
| Two bedroom granny flat, one bathroom | As above plus washing machine and dishwasher | 250L single pump | $3,199 |
| Granny flat plus the main house on one station | Everything on the property | 900L | $4,699 |
Waternex list prices in AUD including GST, current as of August 2026. The Kwikflo 250L is priced by state.
Step up to a Kwikflo 900L Sewer Pump Station only when the station is taking the main house as well as the flat. That is a bigger hole, machine access, and a real excavation budget.
Which unit to buy
Three 250L packages suit a granny flat, and the difference is the pump inside the tank, not the tank. All three arrive pre assembled with the pipework, valves and float gear fitted, so the plumber is connecting rather than building.
Kwikflo 250L Sewer Pump Station
The Kwikflo 250L Sewer Pump Station at $3,199 is the value pick and the one most granny flat builders order. It runs a cutter pump, comes pre assembled, and is priced by state.
REEFE RGM055A 250L Sewer Pump Station
The REEFE RGM055A 250L Sewer Pump Station at $3,305 adds a high level alarm to a compact grinder pump. Buy this one if the flat will be tenanted, because the alarm tells someone there is a problem before the shower does.
REEFE QubeX 250 Series
The REEFE QubeX 250 Series at $3,399 carries the heavier grinder. Worth the extra couple of hundred if the discharge run is long, the lift is towards the top of the range, or you simply want more grunt in the hole than the job strictly needs.
The full range sits in Sewer Pump Stations and the broader Packaged Pump Stations collection.
Head height still decides it
Head height, not tank size, is what makes a granny flat pump station work or fail. Head is the vertical lift from the bottom of the pit to the highest point of the discharge line, plus the friction the pipe run costs you along the way.
Granny flats are the worst offenders because the pipe run is long. The flat is at the back, the junction is at the front, and there is 30 or 40 metres between them. A rough field rule is one metre of head for every 10 metres of horizontal run, plus a bit for each bend. A pit 1.2m deep with a 1.5m climb over a retaining wall and 35 metres of pipe is not a 2.7m job. It is closer to 6 metres once friction is counted.
Size the pump above that figure with margin, never at it. The full method is in how to calculate head height for a pump station, and your plumber should verify it against the actual pipe spec before you order.
Where the station goes on the block
Put the station between the flat and the sewer connection, on the lowest ground, and outside anything anyone will ever drive over. That last part gets ignored and it costs money later.
- Keep it out of the driveway. Standard covers on these packages are pedestrian rated. If the pit ends up under a driveway or a parking pad, specify a load rated cover at order. Expensive once there is concrete over it.
- Leave room to lift the pump out. The pump is the wear item and it will come out one day. A pit tucked 300mm off a boundary fence turns a one hour service into a bad afternoon.
- Check the route in before you order. A 720mm tank goes down most side paths. A 1075mm tank does not.
When a macerator or lifting station is the better answer
A macerator or undersink lifting station beats a buried pump station when you only need to lift one or two fixtures, not the whole flat. Smaller spend, no excavation, and it sits inside the building.
The REEFE REG015 Grinder Macerator Pump at $1,199 handles a single toilet and basin. For a kitchenette or laundry in a conversion, the REEFE QUP Series undersink greywater lifting station at $1,046 or the stainless Kwikflo KUS Series undersink pump station at $1,952 do the job without touching the yard.
The line is simple. Whole dwelling draining to the main, buy the buried station. One fixture stranded on the wrong side of the levels, buy the macerator. Do not run a full flat off a macerator to save two grand. It will not cope.
All of that is sewer. If what you are moving is rainwater or driveway runoff around the new flat, that is a drainage pump, not a grinder, and the unit is the Kwikflo 250L Stormwater Pump Station at $2,607.
What the whole job costs
Budget $3,199 to $3,399 for the equipment, then add excavation, plumbing, electrical and the sewer connection, and the installed total on a straightforward granny flat commonly lands around double the equipment price. That is a range, not a quote, because the site drives it.
What moves the number: excavator travel, sand or rock, the length of the discharge run, how far the switchboard sits from the pit, and what the water authority wants for the connection. The breakdown is in what a sewer pump station really costs in Australia. Builders and plumbers doing volume should look at trade pricing.
Four things that go wrong on granny flat installs
Four errors account for most of the callbacks we hear about.
Sizing on the tank and ignoring the lift. The 250L tank is right. The pump inside it has to suit a 35 metre run, and the cheapest pump often does not.
Measuring to the sewer main instead of the high point. If the discharge line climbs over a retaining wall before it drops away, that peak is your static head, not the main.
Leaving the power off the plan. The station needs a dedicated circuit and an electrician. Work that out at the design stage, not when the tank is already in the ground.
Skipping the high level alarm on a tenanted flat. A tenant will not notice a pump has stopped until the floor waste backs up. An alarm gives you a day of warning.
Frequently asked questions
What size sewer pump station do I need for a granny flat in Australia?
A 250L packaged sewer pump station with a single grinder pump suits a standard granny flat: one bathroom, a kitchenette and a laundry. Step up to 900L only if the same station is also taking the main house.
Does a granny flat always need a pump station?
No. A granny flat only needs a pump station when its drain sits below the sewer connection point and gravity cannot deliver the fall. If the flat is on the high side of the block with fall the whole way to the junction, it drains by gravity like any other dwelling.
How much does a granny flat sewer pump station cost in Australia?
The equipment runs $3,199 to $3,399 for a 250L packaged station as of August 2026. Installed, allow roughly double that on a straightforward site once excavation, plumbing, electrical and the connection are included, and more where access is tight or the ground is rock.
Can a granny flat and the main house share one pump station?
Yes, and it is common on renovations where the existing house drain is already marginal. A shared station has to be sized for the combined load, which usually means a 900L tank rather than a 250L.
Do I need council approval for a granny flat pump station?
Usually yes, and the requirements vary by state and by water authority. Sewer connection for a secondary dwelling is regulated work and your licensed plumber handles the application as part of the connection. Start it early, because approval timing can affect the build program.
Send us the levels and we will pick the unit
Give us the pit depth, the height the discharge has to climb, and the run to the sewer junction, and we will tell you which station fits. Free, and quicker than putting the wrong pump in a hole you have already backfilled.
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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.