Conical Washers (Compression Seals) – Fix Under-Sink Leaks Fast
Conical washers are small rubber or plastic seals used in compression fittings. In UK households, they are the primary seal for most kitchen and bathroom waste pipes. When they wear out, leaks are inevitable.
What do Conical Washers actually do?
In standard UK plumbing (32mm and 40mm waste), conical washers are designed to:
- Create a Watertight Seal: Compression nuts squeeze the tapered end into the fitting to block water.
- Bridge Gaps: Their shape allows them to seal even if the pipes aren't perfectly aligned.
- Vibration Resistance: The flexible material prevents joints from loosening due to water pressure.
Common Signs of a Failed Washer
Because these are made of rubber or soft plastic, they eventually become brittle or flattened. Watch for:
Where to Buy Conical Washers in the UK
Washers are very affordable, typically costing between £1 and £5 for a pack. We highly recommend buying an assorted pack so you always have 32mm (Basin) and 40mm (Sink) sizes on hand.
| Retailer | Stock Status | Benefit | Link |
|---|---|---|---|
| Screwfix | In Stock | Great value bulk packs | View Range |
| Toolstation | Available | Assorted packs for all waste pipes | Check Stock |
How to Replace a Conical Washer
This is a 5-minute DIY fix that can save you a call-out fee. No tools are usually required.
Unscrew the Nut
Unscrew the large plastic compression nut at the leaking joint. Slide the nut back along the pipe to expose the old washer.
Clear the Sealing Face
Remove the old washer. Use a damp cloth to clean any slime or grit from the pipe and the inside of the fitting where the new washer will sit.
The "Pointy" End Faces In
Slide the new conical washer onto the pipe. Crucial: The narrow, tapered end must point toward the fitting (the part the pipe is entering).
Hand-Tighten Only
Push the pipe fully into the fitting. Slide the washer and nut forward. Tighten the nut firmly by hand. Run the water to test for drips.
💡 Pro Tips for a Leak-Free Finish
- Hand-tighten only: Using a wrench on plastic nuts often deforms the conical washer, causing more leaks.
- Always Replace: If you take a waste joint apart, it's best practice to put a new washer in rather than reusing the old, compressed one.
- Size Matters: Basins and bidets use 32mm (1 1/4"), while kitchen sinks and baths use 40mm (1 1/2").