Soil vent pipes (SVP) or ventilated discharge pipe is a vertical pipe that removes waste water from toilets, showers and baths away from your building.
Often attached to the outside of the building just above the roof gutter level. The vents allow odours to be released from the pipe in a way that is not noticeable via a vent. The vented pipes also allow air into the drainage system facilitating the process of aerobic sewage digestion and keeping the waste flowing freely.
These pipes were traditionally made from cast iron, but UPVC is the modern material being durable and strong as well as easier to install.