The 1.2m XPRESS. Nine sizes plus the 900mm.

Every standard 1.2m XPRESS underground tank and the 900mm compact are priced on this page, including GST, and you can order them online. Your Promax rep then confirms the tank and arranges delivery, including delivery to site if you want it.

The 1.9m XPRESS is priced on enquiry. Pricing several tanks or a whole subdivision? Send the tank schedule and we will quote the lot.

The 1.2m and the 900mm are built in the South Island and sold there. The 1.9m is built in the South Island and sold nationwide, with freight quoted with your order wherever the job is.

For a North Island site, ENDURO is the range to start with: it is built in the North Island and covers 1,000 to 10,000 litres. See the ENDURO range.

Every XPRESS underground tank travels free to your nearest Mainfreight depot, free to your site inside the Christchurch Metro area, and you can collect from Promax instead if that suits the job. If you want the tank delivered to site, your Promax rep arranges it and quotes it with your order, so the tank and the freight are priced together before you commit.

Your resource consent or stormwater engineer sets the volume, usually in litres or cubic metres.

If you have that number, go straight to the standard sizes and pick it. If you do not have it yet, send us what you do have and we will tell you what is needed to size it.

The 1.2m covers 2,000 to 10,000 litres and suits most jobs. Because one diameter runs across the range, the hole and the install detail stay the same and only the length changes: 2,000 litres is about 1.95 metres long, 10,000 litres about 8.75.

Choose the 1.9m when the volume is large and the trench cannot be: 10,000 litres sits in 4.25 metres on the 1.9m. Choose the 900mm when access is narrow or the volume is small.

Only with the right lid and riser. The standard polyethylene lid supplied with the tank is for garden areas. For a pedestrian or trafficable area the installation guide calls for a steel manhole lid and a Promax adjustable riser, which takes a concrete surround so vehicle loads are carried by the concrete and not the tank.

The guide has installation drawings for residential driveways (vehicles up to 2,500kg) and commercial driveways (vehicles up to 10,000kg). Anything heavier needs an engineer. Tell us what goes over the top and we will confirm the right lid and riser to order with the tank.

The installation guide sets a 45 degree line of influence that has to start at least 1,000mm from the edge of the house foundations, and at least twice the retaining height away from a retaining wall. Leave a minimum of 150mm between the tank and the excavation wall at the narrowest point. The design assumes the site meets the NZS 3604:2011 definition of good ground; if it does not, or the tank cannot sit outside those limits, a chartered professional engineer needs to look at the site.

Washed crushed stone or gravel with angular particles no larger than 13.2mm, or clean naturally rounded gravel no larger than 19mm, with no more than 5% passing a 2.36mm sieve and a dry density of at least 1,500kg per cubic metre. Do not mix the approved backfill with sand or native soil, bring it up to at least the tank crown, place it in lifts of no more than 300mm, and probe it under the full length of the tank and into the ribs so there are no voids.

The Underground Tank Installation Guide covers handling, location, excavation, backfill, anchoring and manholes, with installation drawings for lawn areas, residential driveways (vehicles up to 2,500kg) and commercial driveways (vehicles up to 10,000kg). The Underground Tank Riser Installation Guide is on the same downloads page, and the dimensions and weight of every size are on its product page.

An empty tank in saturated ground wants to lift. Uplift restraint kits and installation anchors hold it down, and they are sized to the tank: one kit per 1,000 litres on the 1.2 m tanks, and one per 2,500 litres on the 1.9 m.

Stated burial depths in the installation guide assume dry ground with no hydraulic loads, so if groundwater is a known issue on your site, say so when you enquire and it goes into the spec.

Potable water, stormwater retention and detention, and waste storage. A single tank can do two jobs on the same site, holding back stormwater during a rain event and storing water for reuse, as long as the design allows for it. Tell us the application when you enquire and it goes into the spec.

Pro-rata, from the date of purchase, per the Promax Warranty Terms and Conditions: 5 years on standard Promax underground tanks, which includes the XPRESS underground range.

The warranty covers the tank. Lids, fittings and inlet and outlet connections are excluded. The tank must be registered on promax.co.nz within 30 days of delivery.

A drainlayer, working to the Promax Underground Tank Installation Guide that comes with the tank. Excavation, bedding and backfill all matter on an underground tank, and connecting into the drainage is restricted work in New Zealand, so it has to be done by a registered drainlayer.

Your project location, the application, the required volume, site conditions, consent notes, and any plans or outlet specifications you have. Nothing needs to be finalised before you make contact.