How to unblock a drain — the honest, step-by-step guide
What actually works, what makes it worse, and when to stop trying and call a professional.
Identify where the blockage is
The single most useful thing you can do before touching anything is work out where the blockage actually is. Fill each sink, bath, shower and toilet on the property with a small amount of water in turn and see how quickly it drains.
If only one fixture is slow, the blockage is in that fixture's waste run. If everything on one bathroom is slow, the blockage is in the stack for that room. If ground-floor fixtures and downstairs toilets are affected across the property, the blockage is in the underground drain — and that's where DIY tools stop being useful.
Sink and basin blockages — start with the trap
Under every sink and basin is a U-bend or bottle trap. Ninety percent of household blockages sit here. Put a bowl under the trap, unscrew both ends by hand, and empty the contents into a bin bag (never back down the drain).
Scrub the trap out with a bottle brush, replace the seals if they look worn, and reassemble. Test with running water. If the trap was clean but the waste pipe is still slow, run a hand-snake through the horizontal run.
Blocked toilets — do NOT keep flushing
The single worst thing you can do with a blocked toilet is flush it a second time. If water is already rising, one more flush will overflow it.
Turn off the water at the isolation valve behind the pan (the small screwdriver-slot fitting on the incoming pipe). Then use a toilet plunger or a specialist toilet auger. Do not push a coat hanger down the pan — you will scratch the porcelain and lose the hanger.
Bath and shower blockages — it's almost always hair
Lift the plug or grille, use pliers to fish out the visible hair mass in the trap, and put a wire loop or Zip-It tool down the plughole to catch the deeper stuff.
A weekly enzymatic drain treatment prevents the hair-and-soap-scum plug from re-forming. Never use caustic drain unblocker on old lead or copper pipework — it accelerates corrosion.
External drains and manholes — where DIY stops
If your outside gully is overflowing or a manhole cover is popping up during rain, the blockage is in the underground drain. This is not a DIY job.
Do not lift heavy chamber covers without proper lifting keys — they can drop on your fingers or cause a back injury. Do not stick a garden hose down a manhole and hope for the best — you'll flood a downstream chamber.
Call a drainage specialist. A professional with a jetter or rods will clear the blockage in 30–60 minutes without damaging the pipework.
When to stop and call in a professional
Stop trying if: water is coming up in more than one fixture, sewage is escaping outside, you can't identify the location of the blockage, or you've tried the trap and the waste pipe is still slow.
A professional clearance costs less than the water damage from one overflowing toilet, so don't push it.