Baking soda and vinegar for blocked drains: when it works and when it does not

What you need

• Measuring cup
• Saucepan or kettle to heat the vinegar and the water
• Drain plug or a wet cloth
• Rubber gloves
• Cup or small pan to bail out standing water
• Baking soda (bicarbonato sódico), 1 kg bag (1-2 euros in a supermarket or droguería)
• Cleaning vinegar at 8 per cent (1-2 euros a litre)
• Very hot water, 2 litres (not boiling if the pipes are PVC)
• Concentrated washing-up liquid for the final flush

Step by step

1. 1

   Check this is the right case

   The drain must still be draining, even if slowly. If no water is going down at all, this method is useless: go to the kitchen sink, basin or shower guide instead. Make sure you have not used any chemical in the last 24 hours.

2. 2

   Bail out the water and empty the drain

   Scoop the standing water out with a cup until the drain is empty. Remove the strainer or plug so the baking soda can get well in.

3. 3

   Pour in the dry baking soda

   Tip half a cup (about 100 grams) of baking soda straight into the drain, pushing it down with a gloved finger or a spoon. It should sit in the pipe, not in the sink.

4. 4

   Add the hot vinegar

   Heat a cup of vinegar (250 ml) in the pan until hot to the touch, not boiling, and pour it slowly over the baking soda. It will start foaming immediately.

5. 5

   Cover and wait 30 minutes

   Cover the drain with the plug or a wet cloth so the foam works downwards instead of coming up. Leave it 30 minutes. On a basin or bath overflow, pour a second cup of vinegar through the top hole.

6. 6

   Flush with very hot water and washing-up liquid

   Remove the plug, squirt in some washing-up liquid and then pour in two litres of very hot water from the tap or from a kettle left to stand for two minutes. This carries away the grease the foam has loosened.

7. 7

   Test and repeat only once

   Fill the sink and let it empty in one go: it should drain in under 10 seconds. If it is better but still slow, repeat the process once. If there is no improvement, leave the chemistry and move on to the hook, the trap or the auger.

What happens when you unblock a drain with baking soda and vinegar: the chemistry

Baking soda (sodium bicarbonate) is a weak base and vinegar is 5-8 per cent acetic acid. When they meet they react and release carbon dioxide as bubbles, plus sodium acetate and water. The foam you see is that gas escaping. It lasts about a minute, creates no pressure (the gas leaves through the same drain you poured it into) and once the reaction is over, what is left in the pipe is water with a bit of salt. In other words, the effect is mechanical and brief: the foam shifts whatever is loose in the trap and the first 20-30 centimetres.

What it does well: the vinegar dissolves light limescale on the waste and the trap, the baking soda neutralises the fatty acids in soap and the smells, and the very hot water you flush with carries away grease that was still soft. That is why unblocking a kitchen sink with vinegar and baking soda works when the sink is slow because of the last few weeks of grease, and why it clears the smell from a basin or shower trap in a property that has been shut up. It also works as monthly maintenance so grease does not build up in the first place.

What it does not do: it does not dissolve hair (neither vinegar nor baking soda attacks keratin), it does not soften years of grease bound up with limescale, it does not shift a plug of paper in a toilet trap, and it does not reach a blockage 2 metres down the pipe in the wall. If the water is not going down at all, the mixture never even reaches the blockage: it just floats in the standing water.

• Works: slow kitchen sink from recent grease, trap smells, light limescale on the waste and overflow, monthly maintenance.
• Does not work: sink that will not drain at all, blocked toilet, compacted hair in a shower or basin, blockages in the branch pipe or inspection chamber.

Mistakes when unblocking a sink with baking soda and vinegar

The most dangerous mistake is mixing it with other products. Vinegar with bleach releases chlorine gas, which irritates the lungs in a closed bathroom. Vinegar or baking soda after a caustic chemical unblocker produces heat and spitting in the trap. If you have used any other product in the last 24 hours, flush with plenty of water first and, better still, do not use the mixture at all.

The second mistake is pouring it in with the drain full of water. The reaction happens on the surface of the standing water, not at the blockage. Bail the water out with a cup first. The third is mixing it in a glass before pouring: the reaction is spent in the glass and what reaches the drain is salty water. Dry baking soda first, well down into the drain, then the vinegar on top.

And the fourth is expecting it to work in a toilet. The foam in the bowl looks impressive, but the plug of paper is in the porcelain trap and bubbles will not move it; what works there is hot soapy water and pressure, as we explain in how to unblock a toilet.

When to call a professional

If you have tried the mixture twice and the drain is still slow, the blockage is not where the foam reaches. In a basin or shower, the next step is pulling the hair out with a hook; in a kitchen sink, cleaning the trap and running a hand auger. If that does not solve it either, or if several drains fail at once, it needs a drain machine and, for blockages that keep coming back, a camera to see what is in the pipe.

Our fixed prices including the call-out: unblocking a kitchen sink, basin or shower 70-120 euros, a toilet 80-140 euros, with a drain machine 110-180 euros, and a camera inspection 60-120 euros, free if you book the unblocking. Prices in how much drain unblocking costs and the service in drain unblocking. We arrive in 20-45 minutes in Valencia, Alicante, Torrevieja and Benidorm.

Local pages: drain unblocking in Valencia, in Alicante and in Benidorm.

Hard coastal water: where vinegar really does help

The water in Valencia and Alicante is very hard, and limescale is exactly what vinegar dissolves. A cup of cleaning vinegar (the 8 per cent acidity kind, 1-2 euros a litre in any supermarket) down the drain and the overflow once a month keeps the basin waste, the shower trap and the kitchen sink trap free of the crust that grease and hair later stick to. For that preventive use the baking soda is unnecessary: vinegar and hot water are enough.

In second homes in Torrevieja, Calpe or Dénia, when you open the house after months shut up, the traps smell because the water in them has evaporated. There the mixture does work: the baking soda neutralises the smell, the foam cleans the walls of the trap and the hot water refills it. Do it in every drain on the first day and repeat it before you close up again.

Related guides

If the mixture has not worked in the kitchen, follow the five methods in how to unblock a kitchen sink. For hair in the bathroom, how to unblock a bathroom basin and how to unblock a shower drain. And if nothing works, how to clear a badly blocked pipe.