Tree roots do not smash their way into a sound pipe. They exploit weaknesses that already exist — usually the joints between pipe sections, or hairline cracks.
Older Brisbane homes commonly have earthenware (clay) drains laid in short segments with a joint every 600mm or so. Each joint is a potential entry point. As the ground moves and the pipes age, joints open slightly and release water vapour into the surrounding soil. Tree roots are extremely good at finding that moisture.
A root hair finer than a human hair works into the joint. Once inside, it has everything a tree wants — water, oxygen and nutrients — so it thickens and branches rapidly. Over time the root mass can fill the entire pipe diameter, and as the root thickens it acts like a slow hydraulic jack, cracking and displacing the pipe further.
That is why root blockages are progressive: first slow drains once or twice a year, then more frequent blockages, and eventually pipe damage that needs structural repair. Cutting the roots clears the line, but the entry point remains — so roots regrow, typically within six to eighteen months depending on the tree and season.
Long-term fixes target the entry point itself: patch relining over the joint, full-length pipe relining, or replacing the affected section. A CCTV inspection after root cutting shows exactly how many entry points there are and how bad the pipe damage is.