Combination units and how drain cleaning actually works

Drainage networks fail slowly. Silt settles, grease builds, roots find joints and scale narrows the bore. Capacity reduces gradually until a storm arrives and the network cannot carry what it was designed to carry.

Cleaning restores that capacity, and the equipment used to do it is a combination unit.

What a combination unit is

A combination unit carries two systems on one truck: a high-pressure water jetting system that cuts and dislodges material inside the pipe, and a high-volume vacuum system that recovers it. Some units also recycle water on board.

The single-truck arrangement matters. Jetting alone moves a blockage somewhere else in the network. Jetting with immediate recovery removes it.

Why water recycling matters

Jetting consumes a lot of water. A unit that recycles recovered water back into the jetting system extends how long a crew can work before refilling, which reduces cycles off site and keeps productive time on the job. On remote or access-constrained sites that is often the difference between a one-day and a two-day job.

The cleaning sequence

• Access points are opened and the line is assessed
• The vacuum recovers standing water, silt and loose debris from pits and chambers
• Jetting works the line, typically from downstream, cutting material free from the pipe wall
• Dislodged material is recovered into the tank rather than pushed further along the network
• Access chambers are cleaned out and the recovered material is disposed of appropriately
• CCTV inspection is carried out where the condition of the pipe also needs assessing

That last step is worth planning for. A camera cannot report on a wall it cannot see, so inspection after cleaning gives a far more useful record than inspection before it. Running both in one mobilisation is usually the efficient option.

What cleaning is used for

• Scheduled maintenance on council, commercial and industrial drainage networks
• Clearing blockages in stormwater and sewer lines
• Pit, sump, chamber and gross pollutant trap cleaning
• Preparing a line for inspection, relining or repair
• Restoring capacity ahead of a wet season
• Responding to a surcharge or overflow

When a different unit is the right one

Not every drainage job needs a combination unit. Bulk removal of liquid, sludge or slurry without jetting is vacuum loading work, and high volumes are handled more efficiently by a hydro tanker, where tank capacity is the limiting factor.

Where a fault needs physical access, hydro excavation exposes the pipe at the identified position without damaging surrounding services. The full range of units is on the fleet page.

Nozzles and pressure are matched to the pipe

Drain cleaning is not a single setting. Nozzle choice and pressure are matched to the pipe and to the material inside it. A de-silting nozzle moves accumulated sediment, a cutting head deals with root intrusion, and a penetrating nozzle opens a full blockage before the line is cleaned properly.

Pipe condition sets the limit. An old, cracked or deformed line cannot take the same treatment as a sound concrete pipe, which is another reason cleaning and inspection belong together. Cleaning an asset into failure is not a saving.

Environmental and disposal obligations

What comes out of a drain has to go somewhere lawful. Recovered material can include sediment, grease, hydrocarbons and general waste, and it is taken to a facility licensed to receive it.

• Recovered material contained in the tank rather than discharged back to the network
• Disposal at a facility licensed for the material recovered
• Controls to keep sediment and wash water out of stormwater during the works
• Documentation of disposal where a client or council requires it

On council and industrial networks that documentation is often part of the deliverable rather than an extra.

Access and traffic management

Access is the other planning issue. Cleaning works from pits, manholes and inspection openings, and where those are buried, sealed over or missing entirely they have to be found and opened before anything else can happen. On older networks that step can take longer than the cleaning.

Traffic management is often needed as well, because drainage access points sit in roads, car parks and kerb lines. Both are worth confirming before the crew arrives rather than on the day.

On larger networks the practical approach is to clean and inspect in sections across a programme rather than attempting the whole system in one visit.

Recurring blockages are a symptom

If the same line blocks repeatedly, cleaning is treating the symptom. A CCTV inspection after cleaning will usually identify the cause, whether that is root intrusion, a displaced joint, a deformed section or an unrecorded connection, which is what allows a permanent fix to be scoped.

To arrange drain cleaning, inspection or both, request a project quote.