Why a drain blocks — and why it keeps happening
A drain that reblocks every six months is not telling you that you were unlucky. It is telling you there is a defect.
Updated
One drain or several? The question that changes everything
Before any diagnosis, you need to know whether the problem is local or general. Run water in several drains around the house, on different floors if you can.
If only one drain is slow, the blockage is in the branch serving that fixture. If several are slow at once, if water rises in the tub when the toilet flushes, or if the basement floor drain overflows, the problem is downstream — that is the main drain, and it is a completely different job.
The real causes
Each part of the house produces its own kind of blockage:
- Kitchen — grease. It goes down as a liquid in hot water, then hardens on the pipe walls as it cools and traps everything that follows.
- Bathroom — hair and soap residue, forming a mass caught on the trap or the strainer.
- Toilet — wipes, including those sold as “flushable”, and hygiene products that do not break down.
- Main drain — tree roots, which enter through a joint and grow inside, and settling or insufficient slope that leaves water standing.
Why chemical cleaners fix nothing
Over-the-counter drain cleaners generate heat to dissolve the blockage. In PVC, that heat can deform the wall; in cast iron, common in homes built before the 1980s, it accelerates corrosion. That older stock weighs heavily on the South Shore: 63% of dwellings in Saint-Lambert, 57% in Saint-Bruno-de-Montarville and 56% in Longueuil predate 1980.
And when the product fails to clear it, it sits stagnant in the pipe. Whoever opens that drain next, plumber or homeowner, meets a caustic liquid.
Above all, these products attack the symptom. If the blockage returns to the same spot, there is a physical cause — a slope, a joint, a root — and no chemical corrects the geometry of a pipe.