Clearing a blocked drain
Work out how far down the blockage is first. One fixture blocked is local; several blocked at once is the shared run.
Where it backs up tells you where it is
One fixture draining slowly and everything else fine means the blockage is in that fixture's trap or the short branch behind it. That is a plunger or a hand auger job and it needs no drain access at all.
Several fixtures backing up, or a gully overflowing outside, means the blockage is in the shared run they all feed into. Plunging one sink then just moves water about. That is the point at which you open an inspection chamber and use rods.
- One fixture
- Trap or branch. Plunger first, then a hand auger through the waste or the trap.
- Two or more
- The shared soil or waste stack below them. Local tools will not reach it.
- Gully or chamber overflowing
- The underground run. Rods or a jetter, from the chamber downstream of the blockage.
- Gurgling with no blockage
- Usually a vent problem rather than a blockage. No amount of plunging fixes that.
Plunging properly
A plunger works on pressure waves, not on pushing. Most of the force escapes if the overflow is open, so block it with a wet cloth first. There must also be water in the bowl or the sink, because air compresses and water does not.
Then use short sharp strokes rather than long slow ones, and keep the seal intact between strokes. Pulling the plunger off breaks the pressure and starts again from nothing.
- Block the overflow
- A wet cloth held over it. Otherwise most of the pressure goes there instead of down the pipe.
- Water in the bowl
- Water transmits the pressure wave. Plunging into air achieves very little.
- Short and sharp
- Rapid strokes with the seal held. It is the pressure pulse that shifts a blockage, not steady force.
- Stop after a dozen
- If it has not moved, it is not going to. Change tool rather than repeating for ten minutes.
Augers and how they clear a blockage
A drum auger, often called a plumber's snake, feeds a flexible spring coil into the pipe. The head either breaks the blockage up, hooks it so it can be pulled back out, or bores a hole through it that then lets the flow finish the job.
Turn as you push, always. Pushing without turning either stops at the first bend or, worse, buckles the cable back on itself, and a kinked cable is finished. If it will not turn, withdraw a little and try again.
- Turn while pushing
- The rotation walks the head around bends. Pushing alone jams at the first one.
- Do not force a kink
- A cable folded back on itself is scrap, and it can jam in the pipe. Withdraw and reapproach.
- Pull the blockage out where you can
- Hair and grease are better retrieved than pushed further along to reassemble downstream.
- Flush afterwards
- Boring a hole through a blockage is not clearing it. Run water hard for a few minutes to take the rest away.
Rodding an underground run
Rods are screwed together and pushed from an inspection chamber toward the blockage. Always turn them clockwise as you push and never anticlockwise, because anticlockwise unscrews a joint and leaves rods in the drain.
Work from the chamber downstream of the blockage where you can, so the water you release has somewhere to go. Rodding from upstream means whatever clears comes toward you.
- Clockwise only
- Turning back unscrews the joints. Rods lost in a drain are a considerably bigger problem than the blockage.
- Start downstream
- So released water runs away rather than back at you through the chamber you are standing over.
- Plunger head first
- A rubber disc head pushes water at the blockage. Change to a corkscrew or a scraper only if that fails.
- Count your rods
- It tells you how far along the blockage sits, which is worth knowing if it keeps coming back.
A word on chemical drain cleaners
They work on hair and light grease in a trap and they do very little to a solid blockage further along, because they cannot reach it through standing water. Caustic cleaner sitting in a full pipe is then a hazard for whoever opens the trap next.
They also damage some traps and seals over time. Mechanical clearing is more reliable, and it removes the blockage rather than partially dissolving it and leaving the rest to build up again.
- Standing water dilutes it
- The cleaner never reaches a blockage below a full pipe at any useful concentration.
- Tell anyone who follows you
- Opening a trap full of caustic cleaner is how people get chemical burns to the face and eyes.
- Never mix products
- Different cleaners react with each other, sometimes violently and sometimes producing chlorine gas.
- Mechanical first
- A plunger and an auger cost once and remove the blockage completely rather than thinning it.
Frequently asked questions
- What tool is best for unblocking a drain?
- For one slow fixture, a plunger then a hand auger. For several fixtures backing up, drain rods from an inspection chamber. For a recurring blockage, a hydro jetter clears the pipe wall rather than just punching a hole through the obstruction. Match the tool to how far along the blockage is.
- How do I know where the blockage is?
- By which fixtures are affected. One sink draining slowly means the blockage is in its trap or short branch. Two or more fixtures backing up means it is in the shared run below them. A gully or inspection chamber overflowing means the underground drain.
- What is a plumber's snake and how does it work?
- A flexible spring steel cable, usually in a drum with a crank handle, fed into the pipe while being turned. The rotation walks the head around bends and either breaks up the blockage, hooks it so it can be pulled out, or bores through it so the flow clears the rest.
- Why is my plunger not working?
- Usually because the overflow is open, so most of the pressure escapes there instead of going down the pipe. Block it with a wet cloth. Also make sure there is water in the bowl, since water transmits the pressure wave and air just compresses.
- Can I use drain rods on a plastic waste pipe?
- Not indoors, no. Rods are for underground clay and plastic drains accessed through a chamber, and they are too stiff and too large for a 40mm waste pipe. Use a hand auger of the right diameter inside the house, or dismantle the trap.
- Which way do I turn drain rods?
- Clockwise, always, whether pushing or pulling. The rods screw together clockwise, so turning anticlockwise unscrews a joint and leaves a section of rod in the drain. That is a much harder problem to solve than the original blockage.
- Are chemical drain cleaners worth using?
- For hair and light grease in an accessible trap they can work. Against a solid blockage further along they usually do not, because they cannot reach it through standing water at any useful strength. They also leave a caustic hazard for whoever opens the trap next.
- What is a drain camera for?
- Seeing what the blockage actually is and how far along it sits, rather than guessing. It is worth it for a blockage that keeps returning, because a recurring one usually means a damaged pipe, a root intrusion or a bad fall, and none of those are fixed by clearing it again.
