250L vs 900L vs 1200L: Picking the Right Tank
A 250L sewer pump station is the right tank for most Australian jobs: a granny flat, a basement bathroom, a below-ground laundry, a garbage room. You step up to 900L when the station takes everything the house produces, and 1200L when the property is large, the site is light commercial, or you want two pumps in the hole. That is the answer for nine callers out of ten, and the rest of this page is the tenth.
Want your exact size? Our pump station sizing 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.
Worth saying up front: the tank size is not what decides whether the system works. The pump decides that. If you have not worked out your head height yet, read how to calculate head height for a pump station first, then come back and pick a tank.
What tank volume actually buys you
Tank volume buys two things: fewer pump starts, and time before the drains back up when something goes wrong. It does not buy you more flow, more lift, or a longer pump life on its own.
Cycle volume is what matters, not nominal litres
The pump only ever moves the slice of tank between the start float and the stop float, and that slice is the cycle volume. On a 250L station that slice is maybe 80 to 100 litres. On a 900L it is several hundred. Bigger slice, fewer starts per day, and starts are what wear a motor out. A pump that kicks in 40 times a day is working harder than the same pump doing 12.
A bigger tank buys you time in a blackout
A 900L tank gives a household most of a day of normal water use before anything backs up, where a 250L gives you a few hours at best. That matters on rural blocks and anywhere the power drops out regularly in storm season. It is the one argument for going bigger that has nothing to do with fixture count.
250L: the default, and usually the correct one
The 250L station handles a granny flat, a basement bathroom, a below-ground laundry, a garbage room or a small amenities block, and it is the size that leaves our warehouse most weeks.
The tank is 880mm deep and 720mm across the outside, with a 600mm x 600mm gastight poly lid. That 720mm figure is the one people should check before anything else. It fits through a standard doorway and down a normal side path, which decides the job when the install is around the back of an existing house with no machine access.
The tank alone weighs about 25kg without the pump, so two people can walk it into position. The Kwikflo version is certified to AS/NZS1546.1:2008 and approved by NSW Health.
Three options at this size, and the difference is the pump inside:
- Kwikflo 250L Sewer Pump Station, pre-assembled with an ALC750 high head cutter pump. From $3,199 in NSW, VIC, QLD and ACT, $3,299 in SA, $3,410 in WA.
- REEFE RGM055A 250L Sewer Pump Station, compact grinder pump with a high level alarm included. $3,305.
- REEFE 250L QubeX Sewer Pump Station, the heavier duty grinder of the three. $3,399.
If you are weighing the two brands against each other, we wrote that comparison up properly in REEFE vs Kwikflo pump stations.
900L: the whole of house size
A 900L station is what you buy when the pump station takes everything the house produces, not one wing of it. Four bedrooms, two or three bathrooms, kitchen, laundry, the lot.
The tank is 1200mm deep and 1075mm across, weighing about 45kg empty. Note the jump in diameter. At 1075mm the tank no longer goes through a doorway or down a tight side path, so you need machine access to the hole, and that is a bigger change to the job than the extra 650 litres.
The Kwikflo 900L Sewer Pump Station is $4,699 with a single ALC750 cutter pump, and the same tank is available in a dual pump build.
1200L: large homes, light commercial, and the depth problem
The 1200L tank suits large homes, childcare centres and small commercial kitchens, but the number that decides the job is 1600mm of depth, not 1200 litres. The tank is the same 1075mm across as the 900L, so the extra volume is bought entirely in depth.
At 1.6m you are into shoring, potential confined space procedure and a considerably longer day for the excavator. The Kwikflo 1200L Sewer Pump Station is $4,999 single pump, which is only $300 above the 900L. The tanks are close in price. The holes are not.
2000L and dual pump: when a failure is not survivable
Go dual pump when an overflow means the site stops: apartment blocks, commercial buildings, childcare, anywhere a blocked station is a health notice rather than an inconvenience. A dual station runs two pumps in duty and standby through a control panel, so if one fails or the inflow spikes, the second takes over.
The Kwikflo Dual Sewer Pump Station comes in 900L, 1200L and 2000L. The 2000L tank is dual only. Pricing runs from $5,716.28 for the 900L with twin 240V cutter pumps up to $11,028.32 for the 2000L with twin 415V grinders. Three phase models need three phase supply on site, so confirm that before ordering, not after.
The four sizes side by side
| Tank | Depth | Outer diameter | Tank weight | Typical application | From (single pump) |
|---|---|---|---|---|---|
| 250L | 880mm | 720mm | 25kg | Granny flat, basement bathroom, garbage room | $3,199 |
| 900L | 1200mm | 1075mm | 45kg | Whole house, 3 to 4 bedrooms | $4,699 |
| 1200L | 1600mm | 1075mm | 62kg | Large home, childcare, light commercial | $4,999 |
| 2000L | Dual pump only | Dual pump only | 180kg with pumps | Apartment blocks, commercial, civil | $11,028.32 (dual) |
Waternex list prices in AUD including GST, current as of August 2026. The 250L Kwikflo is priced by state. Tank weights are supplier figures for planning only.
Browse the lot in Sewer Pump Stations, or the wider Packaged Pump Stations range if you are still deciding on the configuration.
The excavation, not the tank, is the real cost difference
Moving from a 250L to a 900L adds $1,500 to the tank price and usually adds more than that again to the install. The tank price is the visible number, so it is the one people compare, and it is the smaller half of the decision.
Here is what actually changes when the tank gets bigger:
- Machine access. A 720mm tank can be carried in. A 1075mm tank cannot, so the excavator has to reach the spot, and if it cannot, the job changes shape entirely.
- Depth. 880mm is a straightforward dig. 1600mm brings shoring, spoil handling and possibly confined space procedure into it.
- Ground conditions. Rock, sand or a high water table all get worse the deeper you go. Hydrostatic pressure on an empty tank is a real risk and should be assessed before install.
- Reinstatement. More hole means more concrete, paving or turf to put back.
Get your plumber to price the hole before you commit to the tank. We have seen people spend $300 extra on a 1200L and then spend $3,000 more putting it in the ground. Our full breakdown of the numbers is in what a sewer pump station really costs in Australia.
When to size up, and when to leave it alone
Size up when one of these is true, and not otherwise.
- The station is taking the whole house rather than a single dwelling extension.
- The property loses power often enough that a few hours of buffer is not enough.
- Peak load is genuinely simultaneous, like a childcare centre at pickup time.
- An overflow would shut the site down, in which case you want dual pumps, and dual pumps start at 900L.
- Inflow is unusually dirty or high volume, such as trade waste.
Do not size up because bigger sounds safer. An oversized tank on a low inflow means waste sits longer, which is how you get the odour complaints, and you paid for a deeper hole to earn them.
What if 250L is still too big?
An undersink pump station is the answer when there is no room to dig at all. These sit inside, under a sink or behind a cabinet, and lift greywater or wastewater up to the drain line. The Kwikflo KUS Series Undersink Pump Station comes as a 40L polyethylene unit at $1,952.28, a 40L stainless at $2,018.28 or an 80L stainless at $2,230.80.
Different job, though. An undersink station is for a fitout with nowhere to excavate, not a cheaper substitute for a buried tank on a normal residential connection.
One more thing: sewer or stormwater
The tanks are the same but the pumps are not, and putting a drainage pump on a sewage duty is the most expensive mistake on these systems. A sewer station runs a cutter or grinder pump that shreds solids. A stormwater station runs a drainage pump: more flow, no cutter, and it will block the first time someone flushes a toilet into it.
For rainwater, driveway runoff or basement seepage, the Kwikflo 250L Stormwater Pump Station is $2,607.29, or see the full Stormwater Pit and Pump Systems range.
Frequently asked questions
What size sewer pump station do I need for a granny flat in Australia?
A 250L sewer pump station covers a standard granny flat: one bathroom, a kitchenette and a laundry. Step up only if the discharge run is unusually long or the lift is beyond about 6 to 7 metres, and in that case the fix is a stronger pump, not a bigger tank.
Is a bigger pump station tank always better?
No. A bigger tank means fewer pump starts and more blackout buffer, but it also means a deeper and wider excavation, a higher install cost, and waste sitting longer if the inflow is low, which causes odour. Match the tank to the actual inflow.
How deep do you have to dig for a 900L pump station?
A 900L tank is 1200mm deep, so plan on roughly 1.4m of excavation once bedding and cover are allowed for. A 250L at 880mm needs a little over a metre. A 1200L at 1600mm needs closer to 1.8m and brings shoring into the job.
What is the difference between a 900L and a 1200L pump station?
Both tanks are 1075mm across, so the only difference is depth: 1200mm versus 1600mm. The 1200L holds 300 more litres and costs about $300 more, but the extra 400mm of digging usually costs far more than the tank does.
Can I fit a pump station tank through a doorway?
Only the 250L. At 720mm outer diameter it clears a standard doorway and most side paths. The 900L, 1200L and 2000L tanks are 1075mm or larger across and need machine access to the install position.
When do I need a dual pump station?
Specify dual pumps when an overflow is unacceptable: apartment and unit blocks, commercial buildings, childcare centres, civil works and any site that stops trading if the station backs up. Dual configurations start at the 900L tank and go up to 2000L.
Not sure which one? Send us the numbers
Give us your fixture count, the pit depth, the run to the main and how much side access you have, and we will tell you which tank fits. Free, and quicker than getting it wrong.
Talk to the Waternex team about your site →
Plumbers and builders buying more than one: trade pricing. Full range: sewer and stormwater pump stations.
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. Electrical connection must be carried out by a licensed electrician. Have your plumber confirm sizing, approvals and compliance before you order.