Should you use chemical drain cleaner?

What they are actually good at

Caustic and acid drain products generate heat and can soften soft organic matter. On a slightly slow bathroom basin with a small amount of hair and soap, one dose sometimes does the job.

That is the honest case for them, and it is a narrow one.

Why they usually fail

A properly blocked drain has standing water in it. The product dilutes into that water and never reaches the blockage at working strength.

On grease it does very little, because hardened fat on a pipe wall is not what these products are formulated to shift. On roots or a foreign object it does nothing at all.

The costs people do not think about

• Repeated use is hard on older earthenware and on some seals and joints
• The liquid stays in the pipe, so whoever clears it afterwards is working in it
• Heat generated in a blocked plastic waste can distort it
• It delays the actual fix while the blockage keeps building
• It masks the symptom of a structural problem that needed looking at

What to do instead

For a slow bathroom drain, lift the grate and pull out the hair you can reach. That solves a surprising proportion of them.

For a kitchen sink, the fix is upstream: let fat set and bin it, and wipe greasy pans with paper towel before washing. Boiling water down the sink is a maintenance habit, not a repair.

For anything beyond arm reach, or anything affecting more than one fixture, it is a drain job rather than a bottle job.