Lower Storm Drain Outlets for 90mm Pipe Connections

The final metre of a drainage run can determine whether the whole installation comes together cleanly. When a Storm Drain channel needs to transition into underground stormwater pipework at a lower level, a RELN Slimline Pit provides a compact end-of-run connection point while keeping access available from the finished surface.

Unlike a conventional square collection pit, the Slimline Pit follows the narrow footprint of the Storm Drain system. That makes  RELN | Channel Drains & Pit Base the natural starting point when channels, outlets or pit components are also required, while RELN covers the wider family of compatible drainage products.

What happens above the pit matters just as much as the connection underneath it. RELN offers Slimline Pit configurations with different grate materials, profiles & finishes, allowing the exposed surface to be chosen around pedestrian use, vehicle conditions, surrounding paving & the required load classification.

What Are RELN Slimline Pits?

RELN Slimline Pits are narrow pit components designed to integrate with the Storm Drain channel system & provide a lower connection point for 90mm PVC stormwater pipe.

Rather than treating the end of a channel as an isolated outlet, the Slimline Pit creates an accessible transition between the surface drainage run & underground pipework.

The pit measures approximately:

► 335mm external length
► 121mm external width
► 261mm external depth
► 335mm internal length
► 100mm internal width
► 248mm internal depth

Depending on the configuration, the range can include:

► Slimline Pit base only
► Black plastic grate
► Black heelguard plastic grate
► Portland Grey plastic grate
► Sandstone plastic grate
► Terracotta plastic grate
► Heritage Green plastic grate
► Galvanised grate configurations
► Stainless steel grate configurations
► 316 architectural grate configurations
► Class C ductile iron grate configurations

The pit body establishes the transition below ground, while the selected grate determines how the installation performs at the finished surface.

Why Choose RELN Slimline Pits?

A channel can collect runoff effectively & still leave an awkward connection problem at the end of the run. The Slimline Pit gives installers another way to transition from Storm Drain into underground pipework where a lower outlet position better suits the drainage layout.

Depending on the configuration, a RELN Slimline Pit can help:

► Provide a lower pipe connection at the end of Storm Drain
► Connect with 90mm PVC stormwater pipe
► Maintain continuity with the Storm Drain channel system
► Keep the end connection accessible from above
► Work with different compatible grate configurations
► Suit pedestrian, domestic & selected commercial applications when correctly specified
► Coordinate with different outdoor finishes
► Create a compact transition between channel drainage & underground pipework

Its narrow dimensions also correspond with the Storm Drain channel profile. Instead of introducing a much wider square pit simply to make the underground connection, the Slimline Pit continues the linear form of the drainage run.

Common Applications

Picture a garage approach where channel drainage catches runoff before it reaches the door, but the underground stormwater line sits below the level of the channel. A Slimline Pit at the end of the run provides the transition between those two levels while leaving the connection accessible from above.

Common applications can include:

► Garage entrances
► Residential driveways
► Carport approaches
► Concrete paths
► Courtyards
► Paved outdoor areas
► Side passages
► Storm Drain runs beside landscaping
► Commercial entrances with appropriately specified grates
► Drainage runs requiring a lower 90mm pipe connection

A long side path creates another useful situation. Storm Drain may intercept water travelling across paving before terminating near an existing underground line. Rather than forcing the final channel outlet to dictate the pipe elevation, the Slimline Pit provides additional depth at the transition point.

A small commercial entrance raises a different question altogether. The underground connection may still suit a Slimline Pit, but the grate above needs to be selected around the actual traffic crossing it. That separates pit geometry from surface loading instead of treating them as one decision.

Product Selection Guide

Start With the End of the Storm Drain Run

Before choosing a grate colour or finish, establish what the water needs to do after reaching the final channel.

A Slimline Pit becomes particularly relevant when:

► Storm Drain reaches the end of its run
► The underground connection needs to sit lower
► A 90mm PVC stormwater connection is required
► Access to the transition point is useful
► The installation benefits from retaining the narrow Storm Drain footprint

If a conventional end outlet already creates the correct pipe route, don't complicate the installation unnecessarily.

Compare a Slimline Pit With a Standard End Outlet

Both can sit at the end of a Storm Drain installation, but they aren't interchangeable solutions to every layout.

Choose according to the required outlet position rather than assuming the larger component is automatically better.

Plan the Underground Route Before Fixing the Channel

The visible drainage line should never be planned independently of the pipe that carries the collected water away.

Before installation, establish:

► Storm Drain direction
► Slimline Pit position
► Required pipe level
► 90mm PVC route
► Downstream connection
► Finished surface level
► Surface fall
► Nearby underground services

Knowing where the water is going makes positioning the last section of channel considerably easier.

Use the Lower Connection Where the Layout Requires It?

Extra depth is only useful when it solves an actual connection problem.

The Slimline Pit provides the space needed to transition from the Storm Drain channel into a lower 90mm PVC stormwater connection.

Before cutting or drilling an outlet, check:

► Required connection height
► Pipe diameter
► Downstream fall
► Available excavation depth
► Clearance from other services
► Final pit position

Mark the intended connection before making a permanent opening.

Match the Joining Method to the Component

Storm Drain installations contain different plastic components, so one joining method shouldn't automatically be applied everywhere.

RELN's installation guidance for its polypropylene Storm Drain channels differs from the connection method used with the Slimline Pit.

For the Slimline Pit, follow the manufacturer's instructions for connecting the nominated 90mm PVC stormwater pipe.

Check the component in your hands before reaching for adhesive or sealant.

Choose the Grate Separately From the Pit

The same underground transition can sit beneath very different surface conditions.

Once the Slimline Pit itself suits the drainage layout, select the grate around:

► Pedestrian movement
► Vehicle exposure
► Required load classification
► Surrounding paving
► Appearance
► Maintenance requirements

Pit selection answers the underground question. Grate selection answers the surface question.

Consider Plastic for Suitable Domestic Areas

A residential installation doesn't automatically require a metal surface.

RELN offers Slimline Pit configurations with plastic grates in several finishes, including:

► Black
► Portland Grey
► Sandstone
► Terracotta
► Heritage Green

RELN | Plastic Grates provides the relevant comparison where lightweight construction, colour choice & compatible domestic drainage are priorities.

Always confirm the rating & installation requirements of the exact grate rather than assuming every plastic configuration suits the same traffic conditions.

Consider Heelguard Profiles Where People Cross Regularly?

A garage entrance might see dozens of footsteps between vehicle movements.

Where pedestrians frequently cross the drainage point, grate profile deserves specific attention.

RELN | Heelguard Grates provides the closer comparison where a flatter heelguard-style surface suits the surrounding use.

Potential locations include:

► Pedestrian garage entries
► Courtyard transitions
► Walkways
► Shared pedestrian & vehicle areas
► Frequently crossed outdoor drainage lines

Specify for the people crossing the drain as well as the water entering it.

Use Architectural Grates Where Finish Matters?

Drainage positioned through premium paving doesn't have to look like an afterthought.

For courtyards, entrances & higher-finish external areas, RELN | Architectural Grates provides a comparison with RELN's architectural grate options.

Changing the exposed grate can alter the finished appearance without changing the basic role of the Slimline Pit underneath it.

Step Up to Ductile Iron Where the Required Classification Demands It?

A commercial access area shouldn't inherit the grate specification from a suburban courtyard simply because both use Storm Drain.

RELN offers a Slimline Pit configuration with a Class C ductile iron grate for appropriate applications.

Where traffic conditions require that level of grate, check:

► Exact product classification
► Installation requirements
► Vehicle type
► Vehicle movement
► Surrounding support
► Complete Storm Drain specification

Never transfer the Class C rating of the ductile iron configuration to plastic, heelguard, architectural or other grate options.

Keep the Storm Drain Relationship Clear

Slimline Pits belong within a drainage system rather than functioning as generic standalone boxes.

Storm Drain installations can incorporate:

► Straight channels
► Corners
► T-sections
► Different grate options
► End outlets
► Bottom outlets
► Leaf guards
► Slimline Pits

Plan from where the runoff enters the first channel to where it leaves the final underground connection.

Know When a Traditional Pit Makes More Sense?

Not every low point belongs at the end of a linear drain.

Storm Drain channels intercept runoff across a line, while larger drainage pits can collect water at a point or act as junctions between underground pipes.

RELN | Drainage & Pits provides the more appropriate range when the project needs broader point collection or an underground junction.

Start with the water movement & pipe layout rather than choosing by component size.

Manage Debris at the End of the Run

Everything carried along the channel eventually reaches the outlet end.

Leaves, grit, mulch & sediment can accumulate around the final connection if the drainage line isn't maintained.

RELN | Drain Guards provides related debris-control options for compatible RELN drainage systems.

Check more frequently where channels sit near:

► Garden beds
► Trees
► Gravel
► Mulch
► Unsealed edges
► Areas carrying soil during heavy rain

A clean grate doesn't necessarily mean the outlet underneath is clear.

Set the Grate to the Finished Surface

Extra depth underneath shouldn't create a poor finish above.

Before surrounding concrete or paving is completed, confirm:

► Grate height
► Channel height
► Surface fall
► Pit support
► Required grate classification
► Pipe clearance
► Access for future cleaning

Where concrete preparation or modification forms part of the job, use equipment suited to the material, depth & surrounding drainage installation.

The finished surface should direct runoff into the drainage line without leaving the grate unnecessarily proud or recessed.

Preserve Downstream Fall

Lowering the connection is useful only if the pipe can continue away correctly.

Check that the final arrangement doesn't create:

► Insufficient pipe fall
► An unintended low section
► Conflict with another service
► An awkward downstream connection
► Insufficient pipe cover

The Slimline Pit should improve the transition, not move the problem further underground.

Check Everything Before the Surrounding Work Closes In

Access disappears quickly once paving, concrete & landscaping reach the drainage line.

Before finishing the area, confirm:

► Slimline Pit position
► Storm Drain connection
► Pipe route
► Outlet opening
► Grate selection
► Surface level
► Downstream fall
► Internal cleanliness

Small corrections are easiest while every component is still visible.

Keep Construction Debris Out

An open pit at the end of a channel is a natural collection point for more than rainwater.

Prevent:

► Concrete slurry
► Soil
► Sand
► Aggregate
► Paving offcuts
► Packaging

from entering the pit during surrounding works.

Clear the complete Storm Drain run before commissioning rather than relying on rainfall to flush construction waste downstream.

Test the Completed Water Path

A drainage run can look perfectly straight & still hold water where it shouldn't.

Before handover:

► Introduce water at the upstream end
► Watch flow through the channel
► Check the transition into the Slimline Pit
► Inspect the 90mm outlet
► Look for standing water
► Confirm downstream discharge
► Remove remaining debris

Spring Jobsite Prep Getting Your Gear Ready reinforces the value of checking equipment & working areas before changing conditions expose unfinished problems.

Inspect the Transition Point During Maintenance

When a Storm Drain run begins clearing water more slowly, the final connection deserves attention.

Inspect:

► Slimline Pit base
► Pipe opening
► Final channel section
► Grate openings
► Debris around the outlet
► Downstream flow

The Hidden Cost of 'I Can Get It Cheaper Online looks at why compatibility, maintenance & completing a job correctly can matter more than the initial component price.

A correctly selected transition is far easier to live with than reopening finished work to correct an unsuitable one.

Expert Tips

► Draw the installation from the side. Channel height, pit depth & pipe level are easier to understand in profile than on a plan view alone.
► Identify the downstream pipe before setting the first channel. The final connection can influence the height of the entire drainage run.
► Separate grate choice from pit choice. The pit handles the transition; the grate handles the conditions at the surface.
► Check the final channel section for fall. Water shouldn't stall immediately before reaching the pit.
► Mark the outlet before cutting or drilling. Confirm the pipe level twice before creating the opening.
► Protect the pit during surrounding works. Slurry, sand & aggregate are easier to keep out than remove later.
► Use actual traffic conditions when selecting the grate. Don't choose solely from the appearance of the surrounding paving.
► Photograph the underground connection before backfilling. Future maintenance becomes much easier when the pipe route is recorded.
► Flush the complete run before handover. Water exposes poor fall, trapped debris & outlet problems quickly.

The components nobody sees after handover can determine how reliably the finished job performs. Why Good Fasteners Matter More Than the Tool You Drive Them With explores the same principle: small components deserve proper selection when the completed installation depends on them.