With a blocked drain, the worst damage usually comes not from the blockage but from whatever is used to try to clear it. Caustic soda is the first thing people reach for and the last thing they should use. The sequence below runs from lowest risk to highest, and it usually stops before you get anywhere near chemicals.
First: work out where the blockage is
This is the one step you must not skip, because it determines everything else.
- One drain slow, the rest normal → the blockage is in that drain or its trap. Fixable without a plumber.
- Every drain in the bathroom slow → the blockage is in the stack that connects them. Harder, but still often fixable.
- Water coming up somewhere else when you run this drain → the blockage is in the main line. Call a plumber immediately.
- Damp on the ceiling or wall below → it is already leaking. Shut off the water and call someone out.
If you are not in the first or second group, do not apply anything from the rest of this text. Chemicals poured into a blocked main line stay there, waiting for whoever has to open the pipe.
Step 1 — hot water
A litre or two of hot water, poured slowly, in several goes. It softens fresh grease and soap deposits, and those cause a large share of slow drains in bathrooms and kitchens. For a drain that has only just started to slow down this is often enough; for older, hardened deposits it is not. With PVC pipes do not use boiling water — hot from the tap is enough.
Step 2 — mechanical
A plunger works on pressure, not chemistry. Run a few centimetres of water into the sink or shower tray so the plunger has something to push, and work with short, sharp strokes.
A drain snake is the most effective tool for hair in a shower drain. With a floor drain, lift the grating out and remove whatever has collected in the throat — often that is exactly where the problem is, and it is visible to the naked eye.
Step 3 — mineral granulate
When the mechanical approach does not get there, a granulate based on sodium bisulphate breaks down organic deposits without the exothermic reaction of caustic soda. It does not heat the pipe, it does not attack PVC or rubber seals, and it is compatible with septic systems.
Application is simple: dry granulate into the drain, then a little warm water, then 15 to 30 minutes of contact time and a flush with plenty of hot water. For stubborn blockages it is left overnight. Never mix it with other products — in contact with chlorine-based preparations the acid releases chlorine gas.
| Method | Clears | Risk to the pipework |
|---|---|---|
| Hot water | Fresh grease and soap | None |
| Plunger | Soft blockages | None |
| Drain snake | Hair, solid objects | Small — scratching the glaze |
| Mineral granulate | Organic deposits | Small |
| Caustic soda | Grease, by saponification | High — heat, pipe deformation |
| Sulphuric acid | Almost anything | Very high — to the pipework and to people |
If the drain runs freely but smells
That is not a blockage. A drain that runs normally but reeks has a dried-out trap or biofilm on the walls of the throat. Drain-clearing chemistry solves nothing there — the explanation is in the article on drain smell from a floor drain.
How to stop it happening again
- A strainer on the shower drain — it catches hair before it reaches the trap
- Fat from the pan into the bin, not the sink — in the pipe it cools and settles
- A sink strainer, emptied regularly — without food residue the deposit has nothing to cling to
- In high-traffic buildings, granulate as routine prevention rather than occasional remedial work