Planning the waste
The size of plastic waste depends upon its use
21mm - overflows
32mm - hand basin
40mm - bath and sink
110mm - soil pipe
The installation of a new branch for a soil pipe is best left to a qualified plumber.
At the planning stage, work out the best route for the waste pipe from the new appliance to the plastic soil pipe stack. This collects waste water from appliances. Alternatively, the waste may be fed to a hopper or an outside gulley. With gullies, it is necessary to terminate the waste pipe below the grid, but above the water level inside.
Be certain not to discharge into the surface water drainage system. This is not permissible and leads to pollution.
The pipe should run downhill slightly along its entire length (6mm fall / 300mm length) and be adequately supported by brackets at regular intervals to prevent sagging.
Fitting and connecting the waste pipe
Once the route of the waste has been decided upon, make a check that there will be no obstructions like cables or pipes in the external wall. Also make careful measurements to determine the position of the soil stack outside.
Drill through the wall using a bit of the same size as the external diameter of the new pipe.
Insert a short length of pipe through the wall and assemble the external pipework to the gulley or hopper.
Do not do up the connections at this stage when running waste to a soil stack. Instead, move the new pipework to one side. To make the connection a number of different types of fitting can be used. A strap-on boss type is the simplest to use. Mark and drill the pipe with a hole cutter of exactly the diameter specified for the fitting you have. Place the boss over the hole, following the manufacturer’s instructions and fasten it in place.
Insert the connector piece, which usually has a rubber gasket pre-mounted to provide a watertight seal
Connect to the soil stack and reassemble your external pipe run making the connections. (solvent / pushfit / compression).
Then, once the external waste has been completed, the pipes and fittings for the internal run can be made. Fit supporting clips at regular intervals on all pipework to prevent it from sagging.