Soakaway clogging ➔ causes, how to size the chamber filter and how a filter bag cuts solids ingress. Read the guide now!
Key points at a glance
Water that used to disappear within hours stands for a day. In heavy rain the chamber overflows, on a system that coped for years.
The last row is regularly underestimated. A soakaway in service during construction without protection can take in more solids in a few weeks than in several normal years.
Once the base has clogged, the only remedy is excavation and replacement of the infiltration medium. That is expensive and disruptive.
The first sign is time
Water that used to disappear within hours stands for a day. In heavy rain the chamber overflows, on a system that coped for years.
The cause is nearly always in the same place: the infiltration surface. Fine particles arrive with the water, settle, fill the pores of the ground beneath and form a dense layer. The process is gradual, which is why it is rarely noticed before it is obvious.
Where the material comes from
| Source | Typical material |
|---|---|
| Roof areas | dust, pollen, moss, leaf fragments, roof wear |
| Yards and access roads | sand, grit, tyre wear, winter grit |
| Adjacent planted areas | soil, fine silt after heavy rain |
| Construction phases | cement slurry, fine sand, greatly increased load |
The last row is regularly underestimated. A soakaway in service during construction without protection can take in more solids in a few weeks than in several normal years.
Prevention is far easier than repair
Once the base has clogged, the only remedy is excavation and replacement of the infiltration medium. That is expensive and disruptive.
A filter bag in the chamber works earlier. It catches solids before they reach the base, and the bag is what gets changed. The cost moves from a rare, large intervention to a regular, small one.
The realistic expectation: a soakaway filter prevents further ingress. It does not reverse clogging that has already occurred.
What size is my soakaway?
Measure the clear internal diameter of the chamber ring, usually at the top edge. Standard sizes are DN1000, DN1500, DN2000 and DN2500, and the figure corresponds roughly to the internal diameter in millimetres.
Measure across the opening at the widest point, and measure the ring rather than the cover. For intermediate sizes, oval sections or unusual constructions we make to measure.
Fitting and changing
The bag hangs in the chamber below the inlet so incoming water runs into it. For concrete and masonry chambers a kit of carabiners and heavy-duty anchors is available; the anchors stay set and only the bag changes. For plastic chambers the kit is not suitable and the suspension has to be solved on site.
Three checks before first installation: load-bearing capacity of the wall at the anchor point, clear space below the inlet for the filled bag, and access for the later change.
When to change
An interval in weeks or months cannot be given honestly, because connected area, use and weather decide.
The reliable indicator is drain-down time: how long water stands in the chamber after rain. When that increases noticeably, the bag is loaded. Anyone who inspects the chamber after heavy rain anyway gets this information for free.
After construction phases or unusually heavy ingress, an additional check is worthwhile regardless of the normal rhythm.
Frequently asked questions about a clogged soakaway
These are the questions most often asked by operators and designers
Can I clean a clogged soakaway myself?
Loose sediment can be vacuumed out. A colmated infiltration layer, however, has to be exposed and replaced, which is a job for a specialist contractor. A filter bag helps prevent the same problem from recurring.
Which nominal diameter do I need?
Measure the clear internal diameter of the chamber ring. Standard sizes are DN1000, DN1500, DN2000 and DN2500. For intermediate sizes, we can manufacture to measure.
Is the filter bag reusable?
No. The soakaway filter bag is a single-use product. Once sufficiently loaded, it is removed and disposed of together with its contents.
Can a filter bag also be used in an infiltration pit?
That depends on the construction. Where the bag can be suspended and the inlet is directed into it, the principle may be transferable. It does not apply to open or filled structures. Send us dimensions and photos and we will assess the installation.
How much infiltration capacity will I regain?
None. A filter bag prevents further solids entering the structure; it does not restore an infiltration base that is already colmated. Its benefit is prevention.
Do I also need a settlement chamber?
With a high sediment load, combining both stages can make sense. A settlement chamber works upstream by a different principle, while the filter bag works inside the soakaway itself. Whether both are required belongs in the drainage design.
Still unsure which filter or next step fits?
Send us the medium, dimensions and application. We will help you decide whether a standard product is suitable or whether the case needs a custom solution.
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