The baking soda volcano fix for a blocked kitchen sink

You will need

• Baking soda (bicarb) · Woolies or Coles home baking aisle, ~$1.50 for 500g
• White vinegar · Woolies or Coles, ~$2 for 2L bottle
• Boiling kettle of water · Your own kettle is fine
• Sink plunger (cup-style) · Bunnings, ~$8–$12 — make sure it has a flat rubber cup, not a ball-shaped one
• Old towel or rag · To block the overflow hole in your sink basin

Step 1

Clear the sink and block the overflow

Remove any dishes and standing water as best you can — scoop it out with a cup if needed. Stuff the old towel tightly into the small overflow hole near the top of the sink basin. This forces pressure downward when you plunge instead of letting it escape upward.

Step 2

Pour in the baking soda

Tip about half a cup of dry baking soda directly down the drain. Try to get it as far into the drain hole as possible rather than spreading it around the basin. This is the non-obvious bit — it needs to go in dry first.

Step 3

Follow with white vinegar

Pour half a cup of white vinegar straight down on top of the bicarb. It will fizz up immediately — that reaction is doing real work, loosening grease and food buildup clinging to the pipe walls. Let it fizz and sit for 10–15 minutes, do not rinse yet.

Step 4

Flush with boiling water

Slowly pour a full kettle of just-boiled water down the drain to flush everything through. The hot water melts the loosened grease and carries the debris further down the pipe. Repeat the bicarb and vinegar cycle once more if the drain is still slow.

Step 5

Plunge if still blocked

If water is still pooling, place the cup plunger flat over the drain hole making a firm seal. Push down and pull up sharply about 10–15 times in a row — rhythm matters more than brute force. Run the tap after to check if flow has cleared.

The stop point

If the sink is still blocked after two plunge sessions, or if water is backing up into a second sink or the dishwasher at the same time, stop — you likely have a blockage deeper in the shared drain line and you need a licensed plumber.

If that is where you are: public cost guides put a blocked drain job at $150 to $450 (sources: ServiceSeeking 2026 price guides; Airtasker cost guides (2024, handyman tier); captured 2026-07-12). See the full cost guide.

Mendy calls tradies for you. Your first booking is free, then $3.50 a booking.

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