When choosing an underground tank, the shape of the tank is often overlooked. But for installers and asset owners alike, it has a direct impact on installation time, cost, and long-term performance.
At APD, we’re often asked about the difference between cylindrical tanks and square ribbed tanks. The biggest difference comes down to how they perform during backfilling and installation.
Square ribbed tanks may look efficient above ground, but when placed underground, they create headaches for drainlayers. Flat walls and ribbed sides mean backfill must be placed with extreme care. Every layer of material needs to be compacted evenly around each rib to avoid voids. If compaction isn’t perfect, soil can shift over time, creating uneven stress and risking distortion or collapse.
This level of precision makes installation slower and more labour-intensive. It can also require specialist tools or inspections, adding further cost. For drainlayers working under pressure, even small mistakes can mean call-backs, tank movement, or costly rework.
Cylindrical tanks, by design, are naturally strong. Their curved walls distribute soil pressure evenly in every direction, eliminating the weak points and pressure spots found in ribbed designs. This makes backfilling far simpler and more forgiving, without the same risk of voids or uneven compaction.
For installers, this translates to faster installations with less stress. For asset owners, it provides peace of mind that the tank is stable, compliant, and built to last. Cylindrical tanks are also less prone to distortion, which means pipework remains aligned, performance remains consistent, and the tank does its job safely for decades underground.
Every hour spent backfilling carefully around a ribbed tank adds labour cost to a project. Rework from a poorly compacted ribbed tank can double installation time. In contrast, cylindrical tanks reduce these risks and keep projects on schedule. With fewer points of failure and easier compliance with AS/NZS standards, they offer long-term savings that go beyond the initial purchase.
At APD, our underground tanks are cylindrical by design and manufactured to AS/NZS 4766:2020 standards. Tested and QC-approved before they leave our Wiri site, they give both installers and asset owners peace of mind. With APD, you know your tank will not only go into the ground smoothly but also perform reliably for years to come.
👉 Takeaway: The right tank shape makes all the difference. Cylindrical tanks simplify installation, reduce costs, and deliver long-term reliability — helping projects finish on time and on budget.
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