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Flat roof gully: outlet, leaf guard and overflow

Updated: 23 October 2026

A balcony, a carport, a garage roof or a flat roof does not drain through the black pot you bury under a patio. A flat roof gully is a weathering outlet in the deck: a flange the sheet can dress to, a spigot the downpipe can take, and a guard that stops leaves sitting in the mouth. The only listing of that kind on the [rain gully comparison](/hub/diy-supplies/rain-gully) is Uzman-Versand B0DGGLK2K1, Dachablauf DN70, at £43.36. Prices are the saved amazon.co.uk figures and they move. A qualifying purchase can earn a commission at no extra cost to you. This is not a roof calculation and not a lab test. Updated 22 October 2026.

A balcony, a carport, a garage roof or a flat roof does not drain through the black pot you bury under a patio.

Our top picks

Uzman-Versand Uzman-Versand DN70 flat-roof gully

Best overall

Uzman-Versand Uzman-Versand DN70 flat-roof gully
7.7/10about £43.36
View offer
UK Plastics UK Plastics single-inlet bottle gully

Rank 2

UK Plastics UK Plastics single-inlet bottle gully
9.0/10about £12.47
View offer
n/a Horizontal bottle gully 305 x 155 mm

Best value

n/a Horizontal bottle gully 305 x 155 mm
7.3/10about £33.44
View offer
On this page
  1. 1.Why a yard bottle will not do
  2. 2.A leaf catcher is not a second outlet
  3. 3.What this listing does not prove
  4. 4.After the water leaves the roof

Why a yard bottle will not do

A roof outlet sits between the deck and the sheet so the membrane can seal to a flange. A yard bottle has no flange, and a DN70 spigot is not 110 mm underground pipe. B0DGGLK2K1 is hard PVC, 470 g, 32 × 32 × 25 cm, with a leaf catcher. The model is Dachablauf DN70. A DN50 to DN150 line in the title is the seller’s range, not extra spigots in the box. The bullets say universal adhesive between sheet and flange. The amazon.co.uk line is 4.5 from 23, and the saved reviews are from Germany, Belgium and France. The £12.47 single-inlet gully can sit at the foot of the downpipe. It cannot be the outlet in the roof.

A leaf catcher is not a second outlet

A leaf catcher blocks as well as guards, and one outlet cannot survive that on a parapet. Harmer says not to rely on a single outlet. The Northern Ireland note wants an overflow on a parapet flat roof, and on a secret gutter, where you will notice it. Do not pipe that overflow back into the same downpipe below the blockage. Approved Document H still sets England’s ground order: infiltration, then a watercourse, then a sewer, and rainwater off the foul sewer where a separate surface-water sewer is available. It does not size this outlet. BS EN 12056-3 is not a sticker on the £43.36 gully, and Osma’s catchment figures are not a rating for Dachablauf DN70.
Uzman-Versand Uzman-Versand DN70 flat-roof gully

Testsieger

Uzman-Versand Uzman-Versand DN70 flat-roof gully
7.7/10about £43.36
View offer

What this listing does not prove

Universal adhesive is a bullet, not a list of membranes. Felt, EPDM, GRP and liquid systems do not share one primer. Harmer says prime for the sheet you have. One non-UK review adapted the outlet before bitumen. Another refused to install it. Those texts are not British reviews. Look at the moulding before it is stuck down. No flow rate, no rodding claim and no second outlet are printed. 470 g and 32 × 32 × 25 cm only tell you whether the sump fits. Call a roofer if the membrane is unknown, if you would cut warm-roof insulation, or if the only escape is one hole behind a parapet.

After the water leaves the roof

The downpipe still needs a lawful ground outlet, usually a shoe into a 110 mm bottle or a sealed wall connection. That England and Scotland split is on the rain gully buying guide. DN70 does not become 110 mm in the downpipe. Clear the leaf catcher at least twice a year, Harmer’s minimum, and after autumn gales if a tree overhangs. A clean guard is still one outlet if you never fitted an overflow. Keep this gully in the deck and give a parapet a second way for water to show itself. £43.36 buys a component, not a drainage design.

Common questions

Can I use a 110 mm bottle gully on a flat roof?
No. A 110 mm bottle gully is a ground pot. It has no flange for a roof sheet, and concreting it into a deck does not weather the hole. The roof listing here is DN70 hard PVC with a leaf catcher, set between the substrate and the sheet. The bottle, if you need one, sits at the foot of the downpipe after the water has left the roof.
What size is this listing?
B0DGGLK2K1 is the DN70 variant, model Dachablauf DN70, at £43.36. The saved file gives hard PVC, a leaf catcher, 470 g, and 32 × 32 × 25 cm. DN70 is not 110 mm. A DN50 to DN150 phrase describes the seller’s family of outlets, not extra spigots in this box. No flow rate is printed, so the size is a diameter, not a capacity for your roof.
Will universal adhesive suit EPDM or felt?
The listing does not say. It mentions universal adhesive between the roof sheet and the flange, and it does not name EPDM, felt, GRP or a primer. One non-UK buyer adapted the outlet and used bitumen. If the membrane maker names a primer or refuses hard PVC, follow that maker, or do not bond this gully.
Is a leaf catcher an overflow?
No. A leaf catcher keeps debris out of the outlet, and it is also what blocks. An overflow is a second, visible escape so you notice the blockage before water ponds over a parapet. Harmer says not to rely on a single outlet. The Northern Ireland note wants that overflow where you will see it. Do not connect it back into the same downpipe below the blocked guard.
How often should I clear it?
Harmer’s brochure says inspect roof outlets at least twice a year. A balcony under trees may need more, including after autumn gales, because the guard fills while it does its job. Lift the catcher, clear the sump, and check any overflow at the same time. Clearing the guard does not add a second outlet you never fitted.
Are the reviews British?
The amazon.co.uk page shows 4.5 from 23. The review texts saved for this ASIN are from Germany, Belgium and France. Use the star line as the marketplace count, not as UK householders describing a British winter. Comments about adapting the outlet, or about quality too poor to install, sit in that non-UK sample.

Related pages

Best bottle gully

Rain gully

Bottle gully vs back inlet for a shoe or wall pipe

How to choose a bottle gully: size, inlet and trap

How to install a bottle gully so the grid stays flush

Sources

Public UK sources and the amazon.co.uk listings compared on this page. Scoring method dated 22 October 2026. Updated 23 October 2026.

  1. Approved Document H (England), 2015 (retrieved 22 October 2026)
  2. Scottish Technical Handbook 3.6 (retrieved 22 October 2026)
  3. FloPlast underground drainage (retrieved 22 October 2026)
  4. FloPlast underground drainage FAQs (retrieved 22 October 2026)
  5. Harmer roof brochure (retrieved 22 October 2026)
  6. Northern Ireland roof drainage (retrieved 22 October 2026)
  7. Brett Martin rainwater FAQ (retrieved 22 October 2026)
  8. NHBC Standards 2025, chapter 5.3 (retrieved 22 October 2026)