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How to install a water butt on a plastic downpipe

Updated: 22 October 2026

You already have the butt and a plastic downpipe, and the first wet weekend is the wrong time to find the tap on the ground. How to install a water butt, for this job, means a level base, a tap you can reach, a diverter at the right height, an overflow back to the drain, and an empty tank before a hard frost. The [300 litre water butt comparison](/hub/garden-watering/300-litre-water-butt) shows how the kits differ. Many listings we read on 20 October 2026 omit the stand or the diverter. A purchase through those links may earn us a commission at no extra cost to you. What to buy first is the [buying guide](/hub/garden-watering/300-litre-water-butt/sub/300-litre-water-butt-buying-guide).

You already have the butt and a plastic downpipe, and the first wet weekend is the wrong time to find the tap on the ground.

Our top picks

Strata Strata (Fuzz01)

Best overall

Strata Strata (Fuzz01)
8.2/10about £49.99
View offer
BeGrit BeGrit (ge1883Z1)

Alternative

BeGrit BeGrit (ge1883Z1)
7.1/10about £59.99
View offer
Ward Ward (GN340)

Rank 3

Ward Ward (GN340)
8.8/10about £64.99
View offer
On this page
  1. 1.Base and weight
  2. 2.Tap, lid, and a watering can
  3. 3.Diverter on a plastic downpipe
  4. 4.First rain and winter

Base and weight

Put the butt where a full tank can stand. A full 250 litre butt is about 250 kg of water plus the shell. The Ward GN340 is about 6 kg empty, so the filled column is near a quarter of a tonne on a 54 × 54 cm footprint. The RHS wants that base firm and level. Rocking slabs, unchecked decking, and a balcony whose strength you do not know are stop points. Set the stand before any water goes in. The Ward fits GN175 or GN176, sold separately. A folding barrel has no raised stand. If you are still choosing the type, that split is slimline versus collapsible.

Tap, lid, and a watering can

Fit the tap before the first fill, with the joint where you can still tighten it. The Ward tap arrives loose. The Strata 210 litre lists a tap, and one box arrived without it. The lid has to come off again for cleaning. Leave room above the rim. One Original Organics review says you must turn the stand the right way or the can will not slide under the tap.
Strata Strata (Fuzz01)

Testsieger

Strata Strata (Fuzz01)
8.2/10about £49.99
View offer

Diverter on a plastic downpipe

Mark the inlet height on the plastic downpipe with the tank already on its stand. Wessex Water says cut about 10 mm below that mark. The AquaLogic sheet describes a cut of about 30 mm. Those guides do not match to the millimetre. Follow the kit in your hand. Do not average 10 mm and 30 mm into a third figure. The usual plastic sizes on those sheets are 68 mm round or 65 mm square. If your pipe is cast iron, shared, or unidentified, stop. Do not saw it.

First rain and winter

Watch the first heavy shower with the lid on and a clear route to the drain. A BeGrit middle tap stays weak even when the barrel is full, so some people dip a can through the zip top. A snapped support means empty the tank and stop. Before a hard frost, drain the butt and leave the tap open. Water Butts Direct gives that advice because ice expands. Do not link a second butt until the first overflow already returns down the pipe. Connecting mains water needs an air gap and notification under the Water Supply (Water Fittings) Regulations 1999. That is a plumber.

Common questions

What has to be level before any water goes in?
The base, including the stand if a can must go under the tap. A full 250 litre butt is about 250 kg plus the shell, and the RHS wants that load on firm, level ground. Rocking slabs, an unknown balcony, and a stand that is still a separate purchase are reasons to wait. Fit the tap while the butt is empty, then mark the downpipe.
Where do I cut a plastic downpipe?
Mark the inlet height with the butt on its stand. Wessex Water describes a cut about 10 mm below that mark. The AquaLogic sheet describes a section of about 30 mm. Use the instructions in your diverter kit, because those guides do not match to the millimetre. Sit the diverter level with or slightly above the inlet so a full tank returns water down the pipe to the drain, not onto the wall.
What if the pipe is cast iron or shared?
Stop. The plastic-pipe kits, including the Harcostar rain-trap example at £14.99, are for sizes such as 68 mm round or 65 mm square, and they are not for cast iron. A shared stack, or a pipe you cannot identify, is the same stop. Ask a plumber or the managing agent. Do not cut a downpipe that serves another flat.
Why is the tap only a trickle?
On a folding barrel, a middle tap can stay weak even when the tank is full. BeGrit reviewers describe that, and some dip a can through the top. On a rigid butt, a new trickle is more often a broken tap, a missing washer, or a cross-thread. The 210 litre Strata has at least one report of no tap in the box. Sort the outlet before you blame the gutter.
What do I do before a frost?
Drain the butt and leave the tap open, which is the Water Butts Direct advice, so ice has room to expand. A frost-proof line on a listing is not a lab result for this set. Store a collapsible PVC barrel somewhere frost-free. A rigid butt can stay outside once it is empty and the tap is open.
Can I link a second butt?
Only after the first butt already sends overflow back down the pipe to the drain. A second tank can then take the surplus. Do not add it while the first overflow still sheets down the wall. Linking does not change the need for a level base under each full tank, at about 250 kg for a 250 litre butt plus the shell.
When do I stop and call a plumber?
Stop for cast iron, a shared stack, a balcony or deck you cannot vouch for, and any link to the mains. A mains connection needs an air gap and notification under the Water Supply (Water Fittings) Regulations 1999. Also stop if a support leg has snapped under a full tank. A plastic downpipe, a level base, and a matching diverter are the jobs you can finish yourself.

Related pages

Water butt and a hosepipe ban

300 litre water butt

Best water butt UK: the Ward as top pick in this set

300 litre water butt: what to check before you buy

Slimline water butt versus collapsible: which to keep

Sources

Public UK sources used for hosepipe bans, rainwater quality, storage and winter care. Listing prices, stars and review counts are the amazon.co.uk lines saved on 20 October 2026. This is not a lab test.

  1. Water Industry Act 1991 s.76 (retrieved 20.10.2026)
  2. Thames Water — temporary hosepipe ban (retrieved 20.10.2026)
  3. South East Water — Sussex hosepipe restrictions FAQ (retrieved 20.10.2026)
  4. RHS — collecting and storing water (retrieved 20.10.2026)
  5. Ofwat / Water Regs UK — rainwater case study (retrieved 20.10.2026)
  6. Water Butts Direct — winter care (retrieved 20.10.2026)
  7. Homebase — 330 litre Graf-style kit (retrieved 20.10.2026)
  8. amazon.co.uk — Ward 250 litre slimline (retrieved 20.10.2026)