Chemical drain unblockers are often the first thing people reach for. They can help in a few situations, but they are not a cure-all, and some carry real risks.
How they work
Most products are one of three types:
- Caustic (alkaline), often based on sodium hydroxide. These turn grease into a soapy substance and break down hair.
- Acidic, usually based on sulphuric acid. These are much stronger and are generally sold for professional use.
- Enzyme or biological products, which use bacteria or enzymes to digest organic matter slowly. They are gentler and better suited to regular maintenance than to clearing blockages.
When they can help
- A basin or shower that is slow rather than blocked, where soap and hair are building up near the plughole.
- Light grease in a kitchen waste close to the sink.
When they will not help
- Wipes, sanitary products and nappies. Chemicals do not dissolve these.
- Hardened fat along a long section of pipe, or a blockage in the underground drain.
- Roots, silt, scale or a damaged pipe. No product fixes a structural problem.
- A completely blocked fitting. If water is not moving, the product sits on top of the blockage in a concentrated pool.
The risks
- Burns and fumes. Caustic and acid products can burn skin and eyes, and splash back when water is plunged or rodded.
- Dangerous reactions. Never mix products, and never use one straight after another. Some combinations give off heat or toxic gas.
- Damage to pipes and fittings. Strong products can damage some older pipework, seals and finishes.
- Risk to whoever clears it next. A drain full of caustic water is hazardous to work on. If you have used a product, always say so when you call for help.
Safer things to try first
- Remove and clean the plug, waste and trap.
- Use a plunger, with the overflow blocked on sinks and baths.
- Use a plastic hair grabber in basins, showers and baths.
- Pour hot (not boiling) water to soften soap residue.
Our guide on how to unblock a drain covers these in more detail.
If it keeps coming back
A drain that needs a product every few weeks has a cause that is not being dealt with, often grease build-up or a pipe defect. Professional drain cleaning or drain jetting removes the build-up from the pipe walls, and a camera survey can show whether something else is going on.