The intrusion of tree roots in sewer pipes is probably the most destructive single element that faces those maintaining a sewer collection system today.

http://www.thelonedrainerandpronto.com.au/vaporooter.php

Sewers are aging expensive assets that attract public attention, only when they fail. There are more than 35,000 kms of water and sewer pipes in Sydney and 60% of all collection systems are made up of pipe with a diameter of 9 inches (225mm) or smaller. The potential for tree root intrusion to inhibit flows, produce blocked drains and damage valuable pipes is enormous.

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