The Hydromax siphonic roof drainage system eliminates air ingress into the pipework which helps to accelerate water down the downpipe increasing the speed with which water drains and self-cleaning the pipework as it goes. It is made in three parts, one of metal coated with PVC and two of HDPE. The metal and outer HDPE part are bolted together. There is an HDPE insert covering the joint of the outer parts. HDPE has been used for the plastic parts because of its strength, adaptability, and durability, and because it allows electrofusion coupling which produces permanently leak proof joints and can therefore be used in spaces to which there is no future access or where access is challenging. This kind of drainage system was used widely at the Olympic Park, London 2012.