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Clean vs dirty water submersible pump

Updated: 22 October 2026

Amazon.co.uk bullets can promise 1 mm residual and particles up to 35 mm in the same listing. Clean versus dirty water on a flat suction pump is a free-passage and mode choice. This page sets the types, which UK jobs map where, and why sewage stays out. Buying order sits in the [flat suction pump buying guide](/hub/garden-watering/flat-suction-pump/sub/flat-suction-pump-buying-guide). Open the [flat suction pump comparison](/hub/garden-watering/flat-suction-pump) for the matrix. A purchase through our links may earn us a commission at no extra cost to you. Peter F., editor for DIY & tools, updated this on 22 October 2026.

Amazon.co.uk bullets can promise 1 mm residual and particles up to 35 mm in the same listing. Clean versus dirty water on a flat suction pump is a free-passage and mode choice.

Our top picks

Einhell Einhell GC-SP 3580 LL

Best overall

Einhell Einhell GC-SP 3580 LL
9.0/10about £47.99
View offer
Einhell Einhell GE-DP 7035 LL

Rank 2

Einhell Einhell GE-DP 7035 LL
8.8/10about £68.98
View offer
Kärcher Kärcher SP 16.000 Dual

Alternative

Kärcher Kärcher SP 16.000 Dual
8.8/10about £99.00
View offer
On this page
  1. 1.Clean, dirty and Dual in plain English
  2. 2.Free passage millimetres that matter
  3. 3.Which jobs map to which type
  4. 4.Sewage stays out, and one Dual can replace two pumps

Clean, dirty and Dual in plain English

A clean-water flat suction pump is for clear water and a low residual finish. Free passage is tiny, so grit jams the rotor. In this set the Einhell 350 W clear row is that tool, and UK reviews treat it as cautious in dirty water. A dirty-water submersible passes larger solids, quoted in millimetres, so pond silt and leafy floodwater can move. Ordinary dirty pumps may still leave centimetres unless they also offer a flat mode. A dual body switches dirty free passage and flat pick-up. Einhell GE-DP 7035 LL claims 35 mm, Kärcher SP 16.000 Dual 20 mm, and Gardena 20000 BASIC 35 mm. The VEATON sensor row is not that class: without the strainer it stays in clean water only.

Free passage millimetres that matter

Free passage is the largest solid the pump claims it can pass. Flood & Water Pumps group clean pumps at a few millimetres, garden dirty pumps around the low tens, and sewage-class passage higher still. Those are trade categories, not a lab certificate. Here the split is a clean flat pump with no useful dirty figure versus duals claiming about 20–35 mm. That decides whether leaf stalks leave the hose or stop the impeller. A 35 mm dual is still not a foul-sewage pump. You do not get 1 mm residual and 35 mm solids at once. Set dirty mode while solids move, then flat mode on a hard support. Changing mode sits on how to use a flat suction pump.
Einhell Einhell GC-SP 3580 LL

Testsieger

Einhell Einhell GC-SP 3580 LL
9.0/10about £47.99
View offer

Which jobs map to which type

Clear pools, hot tubs and patio spills usually suit clean flat suction. The clear Einhell value role fits when you buy hose and finish in continuous mode. Pond silt needs dirty free passage first, then flat mode once the water is clearer and the base is firm. A cellar flood with silt washed in wants a dual. Clear water on a smooth floor can stay with a clean flat pump. Conditional ASIN roles sit on the best flat suction pump page.

Sewage stays out, and one Dual can replace two pumps

A garden dual is not approval to pump foul sewage, septic effluent or toilet waste. Those jobs need specialist pumps and often a professional. Live electrics in standing floodwater also leave this category. One dual is usually better than a clean pump plus a separate dirty pump if your year mixes pools and muddy jobs. Two pumps make sense only if the leisure unit must never see silt. In flat mode, give the inlet a hard base. Dual Einhell reviews warn that a soft floor can seal the plate at the 1 mm setting. Neither mode replaces a wide hose or an RCD.

Common questions

What free passage do I need?
Match the largest solids in the water. Clear pool water needs almost none. Pond silt and leafy floods want the Dual claims in the tens of millimetres in this set, about 20 mm or 35 mm. Unknown foul solids are out of scope.
Is dirty water the same as sewage?
No. Garden dirty-water ratings cover silt and debris within the stated millimetres. Sewage and foul effluent need specialist pumps and different rules. A 35 mm Dual claim is not a sewage rating.
When is Dual better than two pumps?
When the same household empties clear pools and muddy ponds or floods. One Dual with a mode change beats duplicating hose kits, unless you insist on keeping the leisure kit spotless and never letting it see silt.
Can clean flat pumps take gravel?
Poorly. UK reviews of clean flat pumps include rotors jammed by grit. Keep gravel out, or choose Dual or dirty free passage. A clean residual claim does not add a solids rating.
Which mode comes first on a pond clean-out?
Dirty mode, or dirty free passage, while silt moves, then flat mode for the last clearer film if the base can sit firmly. Net large debris before it reaches the inlet.
Cellar silt after a flood: clean or dirty?
Dirty or Dual first. Clean flat only if the water stayed clear. Finish by hand if you need the floor drier than the float allows, and stop if electrics are in the water.

Related pages

Pump to empty a paddling pool or hot tub

Flat suction pump

Best flat suction pump UK: mixed jobs or clear water

Flat suction pump buying guide: residual and solids

How to use a flat suction pump: hose, float and RCD

Sources

Public UK sources and the saved amazon.co.uk listings for this set, checked on 21 October 2026.

  1. Kärcher GB submersible pumps overview (retrieved 21.10.2026)
  2. Electrical Equipment (Safety) Regulations 2016 (Great Britain) (retrieved 21.10.2026)
  3. Business Companion: electrical equipment (retrieved 21.10.2026)
  4. Electrical Safety First: garden advice (retrieved 21.10.2026)
  5. HSE: electrically powered equipment (retrieved 21.10.2026)
  6. Flood and Water Pumps: solids handling explained (retrieved 21.10.2026)
  7. Consumer Rights Act 2015 (retrieved 21.10.2026)
  8. Which?: faulty goods advice (retrieved 21.10.2026)