How to Clear a Blocked Drain: A Tradesperson's Guide

A fast, repeatable method for clearing sink, toilet and floor-drain blockages on the job — and knowing when to reach for a heavy-duty cleaner.

Most blockages come down to the same culprits: grease and fat, soap scum, hair, food waste, and the odd foreign object. The trick to clearing them quickly is working in the right order — assess first, go mechanical where you can, and use a strong chemical clearance when the blockage is organic and stubborn.

1. Assess the blockage

Before anything, work out what you're dealing with. Is it a slow drain or a full stoppage? Single fixture or multiple? A single slow sink usually means a local grease or hair build-up; multiple fixtures backing up points to a blockage further down the line that may need rodding or a jet.

2. Clear standing water and try mechanical first

Bail out as much standing water as you can. For accessible traps, a plunger or a hand auger (snake) shifts a lot of blockages without chemicals. For a known grease or organic blockage that won't budge, a strong drain cleaner is faster and reaches what rods can't.

3. Use a heavy-duty cleaner for organic blockages

For grease, soap, hair and paper, a professional-grade cleaner such as One Shot Instant Drain Cleaner dissolves the blockage rather than just poking a hole through it. Used correctly it works in minutes. See our step-by-step One Shot usage guide for dosing and safety.

4. Flush and confirm flow

Once the blockage clears, flush through with plenty of cold water and check the fixture drains freely. Run the adjacent fixtures too, to confirm the line is clear and not just the trap.

5. Prevent the next call-out

• Advise clients against pouring fats and oils down the sink.
• Fit strainers on plugholes to catch hair and food waste.
• A monthly preventative dose of drain cleaner keeps lines flowing and avoids emergency call-outs.