Unblock the drain yourself, and know when to stop

Before you touch anything, go and run the other taps in the house.

That one minute tells you most of what you need. If the kitchen sink is slow but the bath, the basin and the downstairs loo all drain fine, the blockage is local and it's almost certainly within a metre of the plughole. You can fix that yourself in half an hour. If two or more fixtures on the ground floor are backing up, or water rises in the shower tray when you flush the toilet, the problem is out in the main drain run and you're into different territory. Skip to the last section.

The chemical question, answered first

Put the drain unblocker down.

Caustic soda and sulphuric acid products do work on soft organic blockages, sometimes. The problem is what happens when they don't. You're left with a pipe full of standing water that will burn skin and eyes, and now you can't plunge it, because plunging means splashing. You can't take the trap off either, not without a faceful of something unpleasant. Plenty of plumbers will charge extra for a job where the homeowner has already poured chemicals in, and they're right to.

There's a second problem. Repeat doses of caustic cleaner generate heat inside the pipe, and a plastic trap doesn't love that.

Use it as a last resort before the phone call, not the first move. And never in a toilet.

Kit

You want four things in the house, and they'll cost less than one hour of a plumber's time.

• A proper cup plunger. The flat rubber cup for sinks and baths. The bell-shaped one with the extended flange is for toilets. A lot of people own the wrong one and wonder why it doesn't seal.
• A hand auger, sometimes sold as a drain snake. Three metres of coiled steel in a drum with a crank handle. Cheap, and it reaches things a plunger can't.
• Rubber gloves and safety glasses. Wastewater in your eye is a genuinely bad day.
• A bucket, old towels and a washing-up bowl. Not optional. See below.

Drain rods are a fifth item, worth buying if you've got an outside chamber and a house older than you are.

Start at the plughole

Take the strainer or the pop-up out. In a bathroom basin, the pop-up plug usually unclips or twists off, and in some designs you have to reach behind the tap body under the sink and unscrew a small plastic nut to release the rod first.

What comes out will be a grey-black mass of hair and soap. That's the blockage, four times out of five in a bathroom. Pull it out with your fingers or hook it with a bent bit of coat hanger, put it straight in the bin, and don't try to wash it down.

For a kitchen sink, the enemy is fat. Cooled cooking fat sets inside the pipe like candle wax and everything else sticks to it. Very hot water and a good squirt of washing-up liquid, left to sit for ten minutes and then flushed with more hot water, will shift a mild one. Use hot tap water rather than a kettle at a rolling boil if your trap is plastic. Boiling water won't melt it, but repeated doses will soften the joints over time.

Plunge it properly

Most people plunge badly, then decide plunging doesn't work.

Block the overflow. Every basin and bath has one, and if it's open your plunger is just pushing air around a loop. Wedge a wet cloth into it and hold it there, or get someone to press a palm over it.

Put enough water in the sink to cover the plunger cup completely. You're moving water, not air. Water doesn't compress, so it transmits the shock straight to the blockage.

Seat the cup flat over the plughole, press down slowly to expel the air, then pump hard and fast for about twenty strokes. The pull matters as much as the push. Break the seal on the last stroke and see what happens. Repeat twice before you decide it's failed.

Double sink? Block the other plughole first, or you'll just pump the water sideways.

Take the trap off

This is the bit people are frightened of, and it's the easiest job in the house.

The trap is the U-shaped plastic bend under the sink. It holds a small plug of water permanently, which is what stops the drain smelling. It's also where rings, screws and anything heavy end up.

Put the bucket underneath first. I say that as someone who once took a trap off with a bowl held in one hand and discovered that the water in a kitchen waste pipe is grey, cold and genuinely revolting, and that it goes everywhere.

Unscrew the two large plastic collars by hand. They're designed to be hand-tight, so if one won't move, wrap a cloth around it and use grips gently. Lower the trap into the bucket, tip out the contents, and poke a bottle brush or your gloved finger through it. Check the rubber washers are still seated in the collars, then screw it back together hand-tight. Run the tap for thirty seconds with the bucket still in place and watch the joints. A slow drip means a washer has rolled out of position.

Send the auger in

If the trap was clear, the blockage is further along the horizontal run to the soil pipe, and now you need reach.

With the trap off, feed the auger cable into the open pipe going into the wall. Push until you meet resistance, tighten the thumbscrew on the drum, then crank the handle clockwise while keeping firm forward pressure. You're either boring through the obstruction or hooking it.

Go slowly at bends. If it stops dead and won't turn, back off a few inches and try again rather than forcing it, because a cable can kink and jam.

Pull it out slowly. Whatever's on the end goes in the bin, and then you rinse the cable outside, not in the sink you've just cleared.

Toilets are their own job

Stop flushing. Every flush adds nine litres to a pan that's already full, and a bathroom floor covered in that is a much worse afternoon.

Find the isolation valve on the pipe feeding the cistern, usually a small brass fitting with a screwdriver slot. Turn it a quarter turn so the slot sits across the pipe. Now the cistern can't refill while you work.

Bail the pan down to about half full with a jug. Use the flanged plunger, seat it in the throat of the pan, and work it with the same slow-push, hard-pull rhythm. A closet auger is the proper tool if that fails. Its plastic sleeve protects the glaze on the way in.

Outside, and where to stop

If several fixtures are affected, lift the grate on the gully outside the kitchen and clear the leaves and silt from the trap underneath. Then find the inspection chamber, usually a square or round cover in the path or lawn. Lift it with a screwdriver in the slots.

Chamber empty? The blockage is downstream, between you and the sewer. Chamber full to the brim? Also downstream. Either way, that's rods or a jetting van.

If you rod it, screw the sections up tight and only ever turn clockwise as you push. Turn the other way and you'll unscrew a section, leaving a metre of rod stuck in the drain and a much larger bill.

Call someone if you've got sewage rising into a ground-floor shower, if the same drain has blocked twice in two months, if the run is shared with a neighbour, or if the chamber is full and rodding does nothing. Recurring blockages in one spot usually mean roots, a collapsed section or a fallen joint, and no amount of plunging fixes a broken pipe.

Keep a jam jar by the hob. Every bit of cooled fat goes in there and then in the bin, and you'll do all of the above a lot less often.