Downspout Diverter Setup: Step by Step

A downspout diverter sits inside the downspout and redirects water flow into a barrel when the barrel is not full. When the barrel fills, the diverter automatically resumes routing water down the original downspout path. Getting the installation right matters: a poorly cut or seated diverter will leak, bypass the barrel entirely, or direct overflow against the foundation rather than away from it.

A zinc gutter and downspout system. The diverter fits inside a horizontal cut in the downspout. Photo: Wikimedia Commons / CC BY-SA.

What a Diverter Does

Most residential diverters work on a passive pressure principle. When the barrel is empty, water entering the diverter body follows the path of least resistance — through the side outlet and into the barrel. As the barrel fills, back-pressure builds in the inlet hose until the diverter flap routes water back through the lower downspout section rather than into the now-pressurized barrel line.

This prevents barrel overflow at the top fitting, which would direct water directly onto the ground adjacent to the barrel base — and often close to the foundation.

Types of Diverters

Insert-style diverters

These fit inside the downspout through a rectangular cut. They are the most common type sold through Canadian hardware retailers (Home Hardware, Home Depot Canada, Canadian Tire). They work with standard aluminum and vinyl downspouts and are generally compatible with 2×3-inch and 3×4-inch downspout profiles. Confirm your downspout dimensions before purchasing.

Elbow-style (external) diverters

These replace a section of the downspout with a prefabricated fitting that includes a diverter port. They require removing a segment of the downspout rather than just making a single cut. Installation is more involved but can provide a cleaner appearance and better seal.

First-flush diverters

A first-flush diverter routes the initial runoff from the roof — which carries the most debris, bird droppings, and accumulated dust — into a separate chamber before directing cleaner water to the barrel. They are more commonly used when harvested water will be used on edible crops. They add a second maintenance task (emptying the flush chamber) but improve water quality.

Tools and Materials

• Downspout diverter kit (sized to your downspout profile)
• Flexible inlet hose (typically 1.25 cm or 2 cm diameter, supplied in the kit)
• Tin snips or oscillating multi-tool (for aluminum downspouts)
• Utility knife or fine-tooth hand saw (for vinyl downspouts)
• Tape measure and marker
• Drill with appropriate bit for the outlet port
• Hose clamps or fittings (if not included in the kit)
• Level

Installation Sequence

1. Position the barrel. The barrel must sit on a stable, level surface — a patio slab, compacted gravel bed, or purpose-built platform. The tap outlet at the bottom of the barrel needs 15–20 cm of clearance to fit a watering can. A raised platform of 30–40 cm also improves gravity flow if you attach a hose.
2. Mark the cut height on the downspout. The diverter port needs to be above the barrel's inlet port (usually on the lid or upper side). Account for the inlet hose slope — the hose should run slightly downhill from the diverter to the barrel, typically at a 1–2% grade. Mark the center of the cut on the downspout, ensuring the final hose path clears obstructions.
3. Cut the downspout. For insert-style diverters, make a single horizontal cut across the width of the downspout face at the marked height. For aluminum, use tin snips; for vinyl, a utility knife or fine-tooth saw. The cut width matches the diverter body — most kits include a cut template. File or smooth any sharp edges.
4. Insert the diverter body. Slide the diverter into the cut until it seats flush. The outlet port (the hole that connects to the inlet hose) should face the barrel side. Confirm the diverter sits level — a tilted diverter can cause uneven water distribution.
5. Connect the inlet hose. Attach the flexible hose from the diverter outlet port to the barrel inlet. Maintain a slight downward slope throughout the hose run. Secure connections with hose clamps if the kit does not include locking fittings.
6. Install the overflow outlet. If the barrel does not come with a pre-fitted overflow port, drill one approximately 5 cm below the rim. Attach overflow tubing or a length of downspout extension that routes water at least 1.5 m away from the foundation — ideally onto a planted area or gravel trench.
7. Test the installation. Run a garden hose into the gutter above and observe whether water enters the barrel and whether the diverter seals without leaking. Fill the barrel to confirm the overflow routes correctly.

Common Mistakes

• Placing the barrel on soft ground. A full 200 L barrel weighs over 200 kg. Soft soil compresses unevenly, tipping the barrel and stressing the inlet hose connection.
• Hose running uphill. Any section of inlet hose that runs uphill traps water that freezes in autumn and can crack the hose fitting before you remove it for winter.
• No overflow routing. The single most common installation error. Overflowing water must have a defined path away from the house.
• Forgetting a mosquito screen. An open barrel inlet is a breeding site for mosquitoes. Most barrel lids include a screen, but the overflow outlet also needs a mesh cover.

References

• City of Toronto — Rain Barrel Program Requirements
• Environment and Climate Change Canada