DIY How To

Soil Pipe

The soil pipe is the pipe that takes waste water from the toilet into the drain, it is also common to have any waste water from showers, baths and sinks routed into the soil pipe. It may be necessary to replace a soil pipe for a number of reasons, you may have an old cast iron pipe that needs replacing with a modern PVC pipe or it may be easier to replace a previously painted soil pipe that has flaking paint with a new coloured PVC pipe.

Install a Soil Pipe


Soil Measure the vertical height from the hole in bathroom wall down to the stop within the drain. Fit a branch to a suitable length of pipe and cut to the pipe to the measured length. Push the pipe fully into the underground drain until it hits the stop.
Measuring angle of horizontal Fit a pipe into the branch and due to the angle of the branch (normally 92.5°) the pipe needs to be in line with the hole, if the pipe is above the hole measure how much lower the pipe needs to be and cut the measured amount off the main vertical pipe.
Long horizontal run The further the underground drain and vertical soil pipe is away from the hole going into the bathroom, the lower the branch will need to be, cut the vertical soil pipe shorter to ensue there is adequate fall on the horizontal pipe.
Pipe in line with hole Check that the pipe is in line with the hole, now remove the pipe to gain acess to the hole.
Length of pipe to go through wall Measure from the outside of the hole to inside the bathroom, this will normally be about 300mm for a cavity wall, add approx another 300mm so there is enough pipe inside to connect a wc waste connector, cut a length of pipe to suit which includes the neck part of the pipe to accept a bend. The pipe within the bathroom can be cut back later if necessary when the toilet is being fitted.
Pipe and bend Push a bend into the pipe, push the pipe through into the bathroom, turn the bend towards the vertical soil pipe.
Measure distance between bend and branch Measure from the stop within the open bend to the stop within the branch on the soil pipe, cut a length of pipe to suit.
Push bend onto pipe Remove the bend from the pipe going into the bathroom and and fit the bend to the newly cut horizontal length of pipe.
Horizontal Push the pipe into the branch until it is fully up to the stop, now push the bend into the pipe going through the wall into the bathroom. It is sometimes easier if you connect the pipe going through into the bathroom before you secure the pipe to the wall using a suitable pipe clamp.
Soil pipe Continue up from the branch with a length of vertical pipe so that the top of the pipe protrudes above the edge of the roof and fit a cowl to the top.
45 deg bends It may be necessary to fit a couple of 45° bends so the pipe can come away from the wall and up above the rainwater guttering.
Bath, sink and shower pipes going into soil pipe Carry out a similar procedure for connecting up the bath, sink and shower where necessary, always allow for a fall in the horizontal runs to allow the water to flow away easily.
Soil pipe bottom The underground pipe can just be seen level with the top of the concrete, this ensures that the soil pipe can be replaced in the future without disturbing the underground drain.
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