Blocked Drain? What Actually Works, and What Quietly Wrecks Your Pipes

The same pipe before and after relining. A pipe in the condition on the left blocks again and again, whatever you pour down it.

Everyone has a drain remedy. Half of them work. A few of them will cost you a pipe.

We line and repair pipes for a living, so we see the aftermath of the popular ones. Here is an honest ranking, from the ones worth trying to the ones we wish people would stop pouring down the hole.

Worth trying: a kettle of boiling water

For a slow kitchen sink, in the first day or two, boiling water and a squirt of dishwashing liquid does help. Kitchen blockages are mostly congealed fat, and heat plus detergent breaks it up. Pour it in stages rather than all at once, and give it a minute between pours.

It will not touch hair, roots, or anything that has been sitting for weeks. And if your waste pipe is old PVC, use hot tap water rather than a rolling boil.

Worth trying, if you do it properly: a plunger

Most people plunge wrong. Two things make the difference. Fill the basin with enough water to cover the plunger cup completely, because you are pushing water, not air, and water does not compress. And block the overflow hole with a wet cloth, or all your effort goes out the side.

Twenty firm strokes, then check. If nothing shifts after three rounds, the blockage is further down than a plunger can reach.

Mostly theatre: bicarbonate of soda and vinegar

It fizzes. It looks like something is happening. Very little is.

The reaction spends itself in a few seconds and produces water, carbon dioxide and a small amount of sodium acetate. None of those dissolves fat, hair or scale. What actually helps in that routine is the kettle of hot water people pour in afterwards.

If it has worked for you before, it was a very mild blockage and the hot water did it.

Handle with care: caustic soda and shop drain cleaners

These do work on organic blockages, and they are the reason many drains get through a bad week. But they are hot, because caustic soda in water gives off real heat, and that heat can soften older PVC and set grease harder further down the line rather than clearing it. Follow the dose on the packet, never mix two products, and never use them on a drain that is standing full, because you are then sitting on a basin of caustic liquid with nowhere to go.

Please don't: pool acid

We get asked about this often enough that it deserves its own heading. Hydrochloric (pool) acid down a household drain is a bad idea for three reasons.

It attacks the pipe. Cape Town has a lot of older housing stock with cast iron and galvanised steel waste lines, and acid eats both. In homes with asbestos-cement pipe, still common in parts of the older suburbs, it attacks the cement matrix that holds the pipe together.

It often does not work. Acid clears mineral scale. It does very little to a root mass or a fat plug.

And when it does not work, the problem is now worse. Whoever opens that line next, whether that is you, a plumber or us, is opening a pipe full of concentrated acid. Most plumbers will refuse to work on a drain that has had acid poured into it until it has been flushed, and they are right to.

When it is not really a blockage

Here is the part the remedies never cover. If the same drain blocks two or three times in six months, you do not have a blockage problem. You have a pipe problem, and each unblocking is buying you a few weeks.

The usual culprits in Cape Town homes are tree roots finding their way into the joints of old clay or cast-iron lateral lines, a section that has cracked or partially collapsed, or a belly, meaning a dip where the pipe has sagged and solids settle every time. All three cause blockages in exactly the same spot, over and over.

That pattern is the signal. Not the first blockage. The third one in the same place.

What to do about it

A camera inspection settles the question in under an hour: either the pipe is sound and you had bad luck, or there is a defect and you can see it on screen. From there, a damaged section can usually be lined from the inside rather than dug up, with no trench across the lawn and no lifted paving.

If your drain has blocked more than twice this year, that is the conversation worth having, rather than another bottle from the hardware shop.