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How to lay underground drainage pipe

Updated: October 2026

You have a ring-seal plastic pipe, a garden trench, and a fall you have already chosen. The leak usually starts at a sawn end with no chamfer, or at a barrel perched on bricks. This is how to lay underground drainage pipe of that kind: cut square, chamfer, lubricate the spigot, then bed the pipe on granular material. The [underground drainage pipe comparison](/hub/rods-and-pipes/underground-drainage-pipe) is not the worked example. Its solvent-weld listing uses cement, and its corrugated kits are not this joint. The Products Compared editorial team compiled this from maker joint cards and Approved Document H, against sources current on 16 October 2026. It is not a site visit and it is not a shoring guide.

You have a ring-seal plastic pipe, a garden trench, and a fall you have already chosen. The leak usually starts at a sawn end with no chamfer, or at a barrel perched on bricks.

Our top picks

GIONAR GIONAR catch-basin and downspout kit

Best overall

GIONAR GIONAR catch-basin and downspout kit
6.2/10about £20.99
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eco-filtration eco-filtration 110 mm solvent-weld pipe, 1 m

Alternative

eco-filtration eco-filtration 110 mm solvent-weld pipe, 1 m
4.6/10about £19.99
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lcyen lcyen flexible downpipe, 21 to 60 inches

Best value

lcyen lcyen flexible downpipe, 21 to 60 inches
4.0/10about £12.99
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On this page
  1. 1.Cut and joint a ring seal
  2. 2.Bed the pipe so it stays round
  3. 3.Cover, and the jobs this page will not finish

Cut and joint a ring seal

A factory spigot is already shaped. A sawn end is a square edge that will push the rubber ring out of its groove unless you chamfer it. OsmaDrain’s joint card and FloPlast’s 110 mm sequence share an order: cut square, chamfer the spigot, clean both ends, lubricate the spigot rather than the socket, push fully home, mark the pipe, then withdraw it slightly. FloPlast says at least 12 mm. OsmaDrain says at least 12 mm. A drainagepipe.co.uk note says about 10 mm. Use the figure for the system in your hands. Lubricant is part of the joint. Wickes says silicone pipe lubricant, and never washing-up liquid, oil, or grease. Kalsi warns that a seal washed out of place leaks. If the ring sits proud, twisted, or missing after the pull-back, take the joint apart. The eco-filtration listing, B0GFX8F17F, describes solvent-weld adhesive on a 1 m waste pipe. That is a different joint. Do not cement it into a foul run because the title says 110 mm. Sockets face upstream, so flow enters the socket mouth.

Bed the pipe so it stays round

Plastic pipe has little strength until the soil at the sides holds it. A barrel on bricks, or on lumps of dug clay, bears on points and can oval. Kalsi asks for a 100 mm granular bed. drainagepipe.co.uk describes pea shingle no larger than 10 mm and a trench about 300 mm wider than the pipe, so you can pack both sides. NHBC chapter 5.3, a warranty standard rather than the Building Regulations, talks about 4/10 mm bedding for 110 mm flexible pipe and rejects bricks. Pack granular material under the barrel and up the sides. Recess each socket so the collar is not the support. When the sides need support you cannot leave, the job has left DIY.
GIONAR GIONAR catch-basin and downspout kit

Testsieger

GIONAR GIONAR catch-basin and downspout kit
6.2/10about £20.99
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Cover, and the jobs this page will not finish

Table 10, for SN4 thermoplastic pipe of 100 mm to 300 mm on Class S2 bedding, gives 0.6 m to 7 m of cover in fields and 0.9 m to 7 m under roads. A lawn is closer to the field row. A drive is closer to the road row, and 0.9 m is the minimum printed there. Paragraph 2.44 is the shallow case: if you cannot get the cover, the document points to a concrete slab detail. A maker limit of about 4 m does not replace Table 10. The gradient is already chosen. This page will not pick between a 1:80 foul run and a 1:100 rainwater run. Stop when the pipe may be a public sewer, when the trench is under a drive or in the highway, when an extension sits on a mapped sewer, or when the bore is collapsed. Paragraph 2.5 asks for at least three weeks’ notice before a public connection. Scotland and Northern Ireland have their own rules. Treat Document H as the English text.

Common questions

Do I chamfer a factory end?
A factory spigot is already formed. Chamfer the end you cut. A square sawn edge drives the rubber out of the groove. If you cannot tell, look for a moulded chamfer, and chamfer anything that still shows saw teeth.
Which way do the sockets face?
Sockets face upstream, towards the incoming flow. From the head of the run you should look into the socket mouth. A socket facing downhill leaves a lip for solids and fights the way the ring is meant to sit.
How far do I pull the pipe back?
Push the spigot fully home, mark it, then withdraw it by the amount your system prints. FloPlast and OsmaDrain both say at least 12 mm. One trade note says about 10 mm. Follow the card in the box. The pull-back gives the joint room to move. Leaving it jammed home removes that room.
Can I use washing-up liquid?
Wickes specifies silicone lubricant, and rules out washing-up liquid, oil, and grease. Kalsi warns that a seal washed out of place leaks. Pipe lubricant is cheap beside reopening a trench. Keep the kitchen bottle in the kitchen.
What goes under a plastic pipe?
Granular bedding, such as pea shingle no larger than 10 mm, about a 100 mm bed in Kalsi’s note, packed up the sides. Bricks and lumps of dug clay leave the pipe on points. NHBC warranty practice for 110 mm flexible pipe is the same idea, as 4/10 mm material.
How deep in a garden, and how deep under a drive?
Table 10 prints 0.6 m to 7 m in fields and 0.9 m to 7 m under roads, for SN4 thermoplastic pipe of 100 mm to 300 mm on Class S2 bedding. Read a lawn against the field figures and a drive against the road figures. Shallower cover uses the slab in paragraph 2.44.
When is the trench no longer a DIY job?
When you cannot tell whose sewer it is, when the line runs under a drive or in the highway, when the pipe is collapsed, or when the sides will not stand. A public connection needs at least three weeks’ notice under paragraph 2.5. A weekend joint on an identified garden run is the limit of this sequence.

Related pages

Underground drainage pipe buying guide

110 mm underground drainage pipe fall

Clay or plastic underground pipe

Underground drainage pipe kits

Best underground drainage pipe among this Amazon set

Sources

Sources from the research digest, last checked on 16 October 2026.

  1. Approved Document H, 2015 PDF (retrieved 16 October 2026)
  2. GOV.UK Approved Document H (retrieved 16 October 2026)
  3. FloPlast 110 mm system (retrieved 16 October 2026)
  4. Kalsi Plastics: underground 110 mm specification (retrieved 16 October 2026)
  5. Wickes FloPlast 3 m pipe (retrieved 16 October 2026)
  6. Screwfix 110 mm underground category (retrieved 16 October 2026)
  7. Toolstation 110 mm underground drainage (retrieved 16 October 2026)
  8. Ofwat private sewer transfer (retrieved 16 October 2026)
  9. CPDA structural design (retrieved 16 October 2026)