In some systems the drain is for discharge of waste fluids, such as the drain in a sink in which the water is drained when it is no longer needed. In the United Kingdom, plumbers refer to waste water as 'bad water'.
This is under the premise that the water they are moving from one area to another via the use of a drain is not needed and can be removed from the area, like a 'bad apple' being removed from a fruit bowl. In other systems, such as fountains or swimming pools where waste fluid is recirculated, the drain is the input to the recirculating pumping machine. In the last case, there is an obvious safety issue, because many people do not expect to encounter more than the head of water above the drain when touching a drain.
For example, in a recent case, a lifeguard went to the bottom of a pool to retrieve something and his hand got stuck because of the extra pressure from the pump.When there is a recirculating pump, the risk of suction consists of the head of water, plus the suction of the pump (up to a maximum of 1 atmosphere). Źródło: https://en.wikipedia.org/wiki/Drain_(plumbing)
There are three basic types of plastic pipes: Solid wall pipeedit Extruded pipes consisting of one layer of a homogeneous matrix of thermoplastic material which is ready for use in a pipeline Structured wall pipeedit Structured-wall pipes and fittings are products which have an optimized design with regard to material usage to achieve the physical, mechanical and performance requirements.
Structured Wall Pipes are tailor made solutions of piping systems, for a variety of applications and in most cases developed in cooperation with users Barrier pipeedit Pipe incorporating a flexible metallic layer as the middle of three bonded layers.Barrier pipe is used, for example, to provide additional protection for the contents passing through the pipe (particularly drinking water) from aggressive chemicals or other pollution when laid in ground contaminated by previous use. Most plastic pipe systems are made from thermoplastic materials. The production method involves melting the material, shaping and then cooling. Pipes are normally produced by extrusion.1Źródło: https://en.wikipedia.org/wiki/Plastic_pipework#Types