Wastewater and Sewage Storage Tanks
Underground fibreglass (FRP) tanks for sewage storage, emergency storage at pump stations and effluent holding, from 5,000L to 150,000L.
Fibreglass sewage storage tanks
Mullaly makes underground fibreglass wastewater tanks for councils, water utilities, developers and commercial sites. They are used as sewage storage tanks and emergency storage at pump stations, as wastewater holding tanks where there is no sewer, and as effluent tanks on commercial and remote sites.
Single tanks run from 5,000L up to 150,000L for some applications, in diameters up to 3.28m, in single-wall or double-wall versions. Larger volumes are made up of several tanks connected with PVC or fibreglass pipework.
These are storage tanks, not septic tanks. They hold wastewater until it is pumped on to the sewer or taken away for treatment; they do not treat it.
Emergency storage at sewage pump stations
If a sewage pump station stops, through a power failure or a pump breakdown, sewage keeps arriving. Emergency storage holds that inflow until the pumps are running again, so the network does not overflow. The volume needed is set by the water agency's standards and worked out by the designer.
Mullaly FRP sewage pump stations and emergency storage tanks hold a WSAA (Water Services Association of Australia) product appraisal: PA 1020, Issue 4, valid to 20 April 2031. Mullaly pump stations are designed to WSA 04-2022 (Version 3.2), the Sewage Pumping Station Code of Australia.
Because the tanks and the sewage pump stations come from one factory, the wet well, valve pit and storage can be supplied together. Mullaly has made fibreglass pump stations in Australia for over 30 years, each made in one piece and delivered with the pipework fitted.
Wastewater holding tanks and effluent tanks
Where a site has no sewer connection, a holding tank stores wastewater until a tanker pumps it out. Effluent tanks hold liquid from a treatment system before it is reused, dispersed or pumped on. Mullaly tanks are used for both on:
- Subdivisions and residential developments
- Commercial and industrial sites
- Remote and mining sites
- Caravan parks, schools and sporting facilities
On-site wastewater systems are approved by the local council or health regulator, so check their requirements, and the size of tank they expect, before ordering. Where the stored wastewater has to be lifted to a sewer main, pair the tank with a pump station.
Wastewater tank sizes and specifications
| Item | Detail |
|---|---|
| Single tank capacity | 5,000L to 150,000L (the largest sizes for some applications) |
| Larger volumes | Several tanks connected with PVC or fibreglass pipework |
| Diameter | Up to 3.28m |
| Wall | Single wall or double wall |
| Installation | Underground, and select above-ground installations |
| Structure | Integral, high-profile fibreglass ribs, designed for the soil and surface loads on each site. Not limited by the water table |
| Material | Fibreglass (FRP) with resin that contains no fillers. No protective lining or coating needed |
| Accessories | Access risers, manways, inspection ports, FRP inspection ladders, baffles, and inlet, outlet, overflow and vent points |
| WSAA appraisal | PA 1020 Issue 4 (valid to 20 April 2031), held for Mullaly FRP sewage pump stations and emergency storage tanks |
Full details are in the water storage tank technical data sheet (TD_TDS_003). Send us the storage volume and levels from the design and we will recommend tank sizes.
Why fibreglass for wastewater storage
Corrosion resistant
Sewage gives off gases and acids that attack steel and concrete. The fibreglass resists corrosion from the stored wastewater and the surrounding soil, with no lining or coating to maintain.
Watertight
Designed to be 100% watertight, so wastewater stays in and groundwater stays out of the storage volume.
Not limited by the water table
Integral, high-profile fibreglass ribs give the tank its strength and are designed for the soil and surface loads on each site.
No ongoing tank maintenance
The tank structure needs no ongoing maintenance or inspections. Pump-out, screens and any pumps still need their normal servicing.
Light to transport
A large-capacity tank ships on one truck bed and can be installed in remote places and tight footprints.
Made in Australia
Made by Mullaly at Tomago NSW, near Newcastle, and supplied with an installation manual.
Wastewater storage in use
Sydney International Airport, Pier B (2010). For Sydney Water Corporation, Mullaly supplied a wet well, valve pit and macerator combo pump station with two 85kL overflow storage tanks, installed under an aircraft parking bay where an Airbus A380 parks on top. Everything arrived on three semi-trailers and was lifted into place once the excavation was done, then ballasted and backfilled.
North Queensland Stadium, Townsville (2020). A 110kPa Mullaly FRP emergency storage tank was supplied with a fully fitted-out 3m diameter, 6.2m deep wet well and valve pit combo on a busy stadium site.
If you are comparing a fibreglass tank with precast or poured concrete, read fibreglass vs concrete water tanks.
Projects with Mullaly storage tanks
Sydney International Airport Pier B
A wet well, valve pit and macerator combo with two 85kL overflow tanks, under a parked Airbus A380.
2020 · Townsville, QLDNorth Queensland Stadium
A 3m diameter, 6.2m deep wet well and valve pit combo, supplied fully fitted out for a busy stadium site.
Wastewater tank questions
What is a sewage storage tank?
A tank that holds sewage for a period, either as emergency storage at a pump station when the pumps stop, or as a holding tank on a site with no sewer connection until the contents are pumped on or taken away by tanker.
Are Mullaly emergency storage tanks WSAA appraised?
Mullaly FRP sewage pump stations and emergency storage tanks hold WSAA product appraisal PA 1020, Issue 4, published 21 April 2026 and valid to 20 April 2031.
Is a wastewater holding tank the same as a septic tank?
No. A septic tank treats wastewater on site. A holding tank only stores it until it is pumped out. Mullaly tanks are storage tanks.
What size wastewater tank do I need?
For emergency storage, the volume comes from the water agency's standards and the pump station design. For holding and effluent tanks, the council or health regulator and your designer set it. Send us the volume and we will recommend one tank or a set of connected tanks.
Will sewage corrode a fibreglass tank?
No. The fibreglass resists corrosion from the stored wastewater and the surrounding soil, and needs no protective lining or coating.
Can the tank go in high groundwater?
Yes. Mullaly tanks are not limited by the water table. Tell us the groundwater level when you ask for a quote, and follow the installation manual supplied with the tank.
Can you supply the pump station as well?
Yes. Mullaly makes one-piece fibreglass sewage pump stations, so the wet well, valve pit and storage tanks can come from one supplier.
Downloads
- FRP water storage tank technical data sheet (PDF)
- Single-wall water storage tank installation manual (PDF)
More documents are in the resource centre. For other underground uses, see our underground water tanks. Tank Solutions, the group Mullaly belongs to, also carries these tanks as FRP wastewater and effluent tanks.
Download the water storage tank brochure
Enter your email and the brochure opens straight away. We will also email you the link.
Request a quote for a wastewater storage tank
Send us the storage volume, levels and site details from the design, or the pump station specification. We reply to every enquiry within 2 business days.
Or call 02 4964 8270 or email sales@mullaly.com.au