The short answer
A one-off blockage is debris. A blockage that returns every few months means roots, a damaged section, or a drain laid at the wrong fall. Clearing it treats the symptom; a camera inspection finds the cause so you can price the actual repair.
Clearing is not fixing
A jetter or an auger will clear almost any household blockage, and for a genuine one-off that is the whole job. Something went down that should not have, it is gone now, and the drain works.
The signal worth paying attention to is repetition. If the same drain blocks every few months, it is not collecting debris by chance. Something about that drain makes it collect debris, and clearing it again just resets the clock.
The three usual causes
Tree roots. Roots follow moisture, and a drain joint with the smallest weep is a target. They enter at the joint, then grow into the flow and catch everything passing. Clearing cuts the roots back and the drain runs freely again, which is why it works for a while and then does not. The roots are still outside the pipe.
A collapsed or displaced section. Older clay and earthenware drains crack and drop at the joints as the ground moves around them. A displaced joint creates a step for solids to catch on and a low point for water to sit in. Same result: constant re-blocking at exactly the same spot.
The wrong fall. Waste moves by gravity and needs a specific slope to carry solids along with the water. Too flat and the water runs ahead while the solids stay put. Too steep does the same thing for the same reason. This is the cause people least expect, and it is common on drains that were extended or altered for a renovation without being re-graded.
How the cause gets found
A camera down the line. It is unglamorous and it settles the question in one visit: you can see whether there are roots, where the pipe has dropped, whether there is standing water in a section that should be running clear, and how far along the run the problem sits.
The reason this matters commercially is that it converts an open-ended problem into a priced job. Without it you are buying clearing visits indefinitely. With it you know whether you are looking at a repair to one section or a replacement of a run, and you can decide accordingly.
What repair involves
Depends on the cause and the access:
- Roots at a joint need the joint dealt with, not just the roots cut. Sometimes that is a section replacement, sometimes a reline.
- A collapsed section gets cut out and replaced, or relined where the surrounding pipe is sound enough to take it.
- Wrong fall means the run gets excavated and re-laid to the correct grade, which is the same work as a drainage renovation and is genuinely the only fix.
Relining avoids most of the digging and suits long runs under paving or a slab. Dig and replace is often cheaper on a short accessible run in a garden bed. Neither is automatically the right answer.
Signs worth acting on early
- More than one fixture draining slowly at once, which points at the main line rather than a single trap
- Gurgling from a floor waste or a nearby fixture when something else drains
- Damp or unusually green ground along the line of the drain in dry weather
- The same drain blocking on a rough schedule
Any of those is worth a camera rather than another clear.