Long Drain Runs: Planning Strip Drainage Over 3.6 Metres

Standard drains are built around standard lengths. The moment a project needs drainage across a wide driveway, a commercial forecourt or the full perimeter of a pool, the run outgrows what off the shelf products can do cleanly, and the way the drain is manufactured starts to matter as much as the drain itself.

This guide covers how long drain runs are made and installed: when a run can be manufactured as a single piece, how longer runs are joined, how to handle fall across the distance, and how many outlets a long run needs.

What counts as a long run

Our cutoff is practical. A strip drain can be manufactured as one continuous piece up to 3640mm. Anything past that is a long run, and it needs to be planned as joined sections rather than ordered as a single product.

Long runs come up constantly on commercial and larger residential projects: driveway crossings and vehicle entries, forecourts and loading areas, pool perimeters, and warehouse or factory wet areas. In all of these, the drain has to perform as one continuous channel even when it can't be transported as one.

One piece up to 3640mm is always the first preference

Every join in a drain run is a potential leak point and a visual break in the grate line. A single piece drain arrives welded and tested from the workshop, and installs as one unit with one set of levels to get right.

So if your run measures under 3640mm, order it as one piece, even if the length is unusual. That is exactly what a custom drain is for: manufactured to the millimetre, with the outlet where your plumbing needs it.

Over 3.64 metres: how joined runs work

Runs longer than 3640mm are manufactured as matched sections and aligned on site. Because the sections come out of the same workshop against the same specification, the channel profiles line up and the grate pattern continues without a visible step. The joins land where we plan them, at positions that suit the install, the levels and the plumbing below.

Compare that with building a long run out of off the shelf one metre channels. Every metre adds another joint made up on site, the grate pattern drifts out of alignment, and the finished run looks like what it is: a workaround.

Section lengths also account for transport and site access. A seven metre run might be manufactured as two 3.5 metre sections so it can actually get to the slab it's being cast into. We work this out at quoting stage, before anything is fabricated.

Getting the fall right over a long run

There are two falls at play. The first is surface fall: the pavement or deck graded toward the drain, where around 1 percent is enough. The second is fall within the channel itself, because once water is in the drain it still has to travel to the outlet.

On a short drain, a flat channel empties fine. Over a long run, a flat invert can leave standing water sitting in the channel between cleans, which means odour, sediment and staining. Building a fall to outlet (F2O) into the channel keeps water moving along the full length of the run. Our F2O guide explains how it works and when to include it.

How many outlets does a long run need

A single outlet serving a very long channel means every drop of water travels the full distance before it leaves. In heavy rain, the far end of the channel can fill faster than it empties.

Splitting the run into catchments, each with its own outlet, shortens the travel distance and shares the load across the stormwater connections. On a seven metre driveway run, that might mean two outlets positioned to match the pits below. The right count depends on channel size, expected flow and what the plumbing allows, and it's one of the first things we work through when quoting a long run.

Outlet positions are measured from one end of the run to the centre of each waste pipe, the same way as any custom drain. Our guide on how to measure and specify a custom strip drain covers those fundamentals step by step.

Choosing a grate for a long run

Wedge wire is the usual answer for long outdoor runs. It handles high flow, stands up to traffic, and stays slip resistant underfoot, which suits driveway drains, forecourts, pool surrounds and loading areas.

Where a long run crosses a public walkway or building entry, a heel guard grate keeps the openings small enough that heels and walking aids can't catch in the slots.

Tile insert grates carry the surrounding tile or stone through the drain line, which suits long runs across designed outdoor areas where the drainage should read as part of the floor rather than a fitting in it.

Getting a long run quoted

You don't need drawings to start the conversation, though we'll happily work from them. Send us the total run length in millimetres, the application, the outlet positions and pipe sizes, the depth available in the slab or screed, and your grate preference. A sketch with measurements photographed on your phone does the job.

Every drain is manufactured in our Sydney workshop, so we can talk directly with your builder or plumber about section lengths, join positions and falls before fabrication starts. Send through your measurements or fill in an order form and we'll take it from there.