How to locate and clear a blocked sewer drain

🔧 Trade Guide: How to Locate and Clear a Blocked Sewer Drain

What is involved in locating and clearing a blocked sewer drain?

Blocked sewer drains are a common urgent plumbing callout that require systematic diagnosis, safe clearing methods and compliance with Australian plumbing practice. Plumbing work in Australia must be performed by a licensed plumber. This guide explains the process and helps you select the right tools and materials.

This guide is written for Australian trade professionals and covers fault confirmation, locating the blockage, selecting the appropriate clearing method, verifying line condition and restoring flow in accordance with the PCA and AS/NZS 3500 principles. Where excavation, repair or gas-adjacent work is involved, ensure the relevant licensed trade and service location requirements are followed.

What skill level is required to clear a blocked sewer drain?

Advanced — Estimated time: 1-4 hours for diagnosis and clearing, longer if excavation, repair or replacement is required

What tools are essential for clearing a blocked sewer drain?

What materials are needed for sewer drain clearing?s Required

Safety Requirements

Step-by-Step Guide

Step 1: Confirm the blockage and gather site history

1️⃣ Confirm the symptoms

Establish whether the blockage is affecting a single fixture, a branch drain or the main sewer. Ask about gurgling fixtures, surcharge at the ORG, overflowing gullies, repeated blockages, tree root history and any recent civil or renovation work.

Check whether wastewater backs up at the lowest fixture, external gully or boundary shaft. This helps determine whether the restriction is upstream or downstream of key access points.

💡 Repeated surcharge at the external ORG commonly indicates a downstream main drain obstruction rather than a local branch issue.

Step 2: Isolate the section and identify the best access point

2️⃣ Select safe and effective access

Locate the property sanitary drainage layout using site plans if available. Identify the most suitable access point: ORG, boundary trap/shaft, inspection opening, upstream shaft or stack access where appropriate.

Avoid removing fittings under pressure or where surcharge could discharge into occupied areas. Open access points carefully and observe standing water level, flow condition and any evidence of solids, grease or roots.

Choose the access point that allows the clearest downstream run and minimises mess, property damage and cable turns.

Step 3: Perform an initial visual assessment

3️⃣ Assess flow condition

Once access is opened, determine whether the line is:

Inspect surrounding ground for signs of settlement, odour, persistent wetness or previous patch repairs. These often indicate a broken or displaced drain rather than a simple soft blockage.

If multiple fixtures are affected and the downstream shaft is dry, the issue is usually between the building drain and that downstream point.

Step 4: Use CCTV to locate the blockage

4️⃣ Camera the line before aggressive clearing where possible

Run the CCTV drain camera from the nearest practical upstream point. Record:

A camera-first approach is especially valuable on repeat blockages, older earthenware drains, suspected root intrusion and sites where excavation may be needed. Use the sonde locator to mark the blockage position and line path on the surface.

💡 If the camera cannot pass standing sewage, note the water level and use a machine or jetter to create initial relief before re-camering.

Step 5: Choose the correct clearing method

5️⃣ Match equipment to the obstruction

Use the clearing method suited to the blockage type and pipe condition:

Avoid over-aggressive mechanical cutting in fragile earthenware or known broken pipe sections. If the camera identified collapse or major displacement, plan repair rather than forcing cables through.

Step 6: Clear the blockage with a drain machine

6️⃣ Mechanical clearing procedure

Where using an electric drain machine:

For roots, start with a smaller spear or boring head to establish passage, then follow with a larger root cutter sized appropriately to the drain.

Do not rely on a machine alone for final root removal if the line serves a main sewer and root mass is significant. Follow with jetting and CCTV confirmation.

Step 7: Clear and flush with a high-pressure jetter

7️⃣ Hydro-jet the line

Set up the jetter with the correct hose and nozzle:

Jet from a safe access point, maintaining hose control at all times. Advance slowly to the obstruction, allow the nozzle to work, then retrieve in stages to wash debris back to the access point or downstream discharge location.

Flush until the line runs clear and free-flowing. In long main drains, multiple passes are often required.

⚠️ Never use excessive pressure in damaged pipework or where fittings are unstable. Verify pipe condition first wherever possible.

Step 8: Re-camera the drain and verify condition

8️⃣ Confirm the line is fully serviceable

After clearing, run the CCTV camera again to confirm:

This step separates a true clear from a temporary relief. Many repeat sewer blockages are caused by underlying defects that are only identified after cleaning.

Record footage and stills for the client file, insurance support or quoted repair works.

Step 9: Locate and mark defects for repair if required

9️⃣ Mark repair points accurately

If the line has a break, displaced joint or collapsed section, use the locator to mark:

Repairs may involve local excavation and replacement with compliant PVC DWV or other suitable drainage material to AS/NZS 1260 and installed to AS/NZS 3500 fall and bedding requirements.

Where defects are outside property boundaries or in authority assets, refer to the relevant water authority procedures.

Step 10: Test, reinstate and advise the client

🔟 Final commissioning and reporting

Run multiple fixtures or carry out a controlled flush test to confirm stable flow. Refit all caps and access covers securely, clean and disinfect the work area, and ensure no sewage residue remains.

Provide the client with:

For recurring root intrusion, recommend programmed maintenance or permanent repair rather than repeated emergency clearing.

Common Mistakes to Avoid

Pro Tips

Recommended Tools

🔒 Licensing

Plumbing work in Australia must be performed by a licensed plumber. This guide explains the process and helps you select the right tools and materials. Licensing and compliance requirements vary by state and territory, including NSW Fair Trading, VIC VBA, QLD QBCC and WA Building Commission. All sanitary drainage work must comply with the PCA and relevant parts of AS/NZS 3500. Gas work requires a separate gas fitter licence.