How to connect drain pipe to sewage

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Never cut corners with drainage. You don't want waste water flowing into a garden or above ground. If you’re thinking of installing a new sink, shower, bath or toilet, plan ahead. Work out where you are going to direct the waste water and how you are going to connect the drainpipe to the main sewage outlet.

The process varies from home to home, and depends on access to the sewage pipe and whether it’s plastic, cast iron, concrete or clay. But there are general principles you can follow to make the job as straightforward as possible.

Find and expose the sewage pipe. You may be able to locate the pipe inside your home. This applies particularly to modern houses. The pipe may, for instance, run behind a plasterboard wall from an upstairs toilet. In other homes, sewage pipes may run down the length of the house outside.

Find the sewage inspection chamber if you cannot locate the sewage pipe, or if the pipe is inaccessible. The inspection chamber may be in your front or back garden. A steel, plastic or concrete lid usually covers it. Lift the lid and establish the direction the sewage pipe comes from your home. Dig carefully around the pipe at the point where you wish to connect the drainpipe.

Drill a starter hole in the exposed sewage pipe. The drill bit must match the material of the pipe, which may be plastic, concrete, iron or clay. Drill with care. There’s a risk the pipe may fracture.

Use a jigsaw or hacksaw blade on a plastic pipe to enlarge the hole to the size of the saddle joint. This is the joint that connects the drainpipe to the sewage pipe. For pipes other than plastic, use the appropriate drill bit to create a circle of holes close to each other. The holes must match the diameter of the saddle joint. Gently tap the centre of the circle to break into the pipe.

Put the saddle joint in place and seal it with solvent weld, which is a type of glue you apply to the joint with a brush. The glue sets to create a watertight seal. Some saddle joints come with rubber seals and don’t require solvent weld.

Attach the drainpipe to the end of the saddle joint with a universal rubber coupling. Tighten the coupling in place with the screws on the adjustable collars. If you prefer, use a plastic coupling that slides over the join between the drainpipe and the saddle joint. Seal the plastic coupling with solvent weld.

Connect the drainpipe directly into the inspection chamber if you prefer. Expose the inspection chamber by digging up the ground around it. Drill and cut a circular hole in the side of the chamber and install a saddle joint. Run the drainpipe underground to the inspection chamber and ensure the waste water flows downhill towards the chamber.