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How to use a flat suction pump

Updated: 22 October 2026

You have unboxed a low-level submersible, the hose is still on a separate shopping list, and the float switch looks like an afterthought — yet that float decides whether you finish with a wipe-dry film or stop with centimetres left. This how-to covers kit prep, outdoor RCD power, hose size, float versus continuous mode, placement and shut-down for UK garden use. Ranking stays on the [best flat suction pump](/hub/garden-watering/flat-suction-pump/sub/flat-suction-pump-best) page. Start from the [flat suction pump comparison](/hub/garden-watering/flat-suction-pump) if you still need to pick a model. 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.

You have unboxed a low-level submersible, the hose is still on a separate shopping list, and the float switch looks like an afterthought — yet that float decides whether you finish with a wipe-dry film or stop with centimetres left.

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
VEATON VEATON FSP750C-A

Alternative

VEATON VEATON FSP750C-A
8.0/10about £69.99
View offer
On this page
  1. 1.What to have ready before you plug in
  2. 2.Automatic float versus continuous flat finish
  3. 3.Placement, inlet sealing and dry-run limits
  4. 4.After the job

What to have ready before you plug in

Know where the water will go before the pump moves hundreds of litres: a soakaway you may use, a permitted drain, or a temporary tank. Lay out a wide hose that matches the outlet, often about 25 mm or larger, plus clips or the maker's Quick Connect. Most listings in this set do not include a hose. For soft liners, have a grid, tile or board so the bottom inlet cannot seal shut. Clear Einhell reviewers keep the pump off soft bases. Dual flat mode has the same risk at a 1 mm setting. Use a tested RCD-protected outdoor supply. Electrical Safety First advises that for garden electrics, and HSE treats a 30 mA RCD as secondary protection. The plug should be a UK 13 A BS 1363 fit. Do not force a European plug into a socket, and do not handle connections with wet hands.

Automatic float versus continuous flat finish

Automatic float mode is for bulk removal while you stay nearby. The float cuts power well above the millimetre residual on the box. UK reviews of clear flat pumps measure that cut-off in centimetres, and Dual reviews complain about early cut-out when the float is not adjusted. Continuous mode locks or clips the float so the pump runs into the shallow film. Kärcher SP-class notes reserve the lowest residual for manual operation with a suitable hose. Clip the float only while you watch. It is not a set-and-forget cellar system. If the pump stops with water still visible, check the float, hose kinks and whether you are still in auto. Then switch to continuous and unplug as the stream breaks into air. Clean versus dual sits on clean vs dirty flat suction. Buying trade-offs sit in the flat suction pump buying guide.
Einhell Einhell GC-SP 3580 LL

Testsieger

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

Placement, inlet sealing and dry-run limits

Lower the pump with the hose already clipped. On Kärcher Dual reviews the plastic outlet clip knocks off in murky water, and without it the elbow will not hold. Use dirty free passage for silt, and flat pick-up only when the surface can support the seal. If flow collapses on a soft liner, lift the pump or slide a grid under it. Grit under a clean-water impeller jams rotors. On the VEATON sensor pump, residual depth is not the automatic start depth. Never leave continuous mode unattended on an empty floor. Dry-running cooks seals. Hot plastic, repeated RCD trips or a damaged cable mean you unplug and inspect.

After the job

Unplug before you lift or open the pump. Flush dirty-mode units with clean water after pond or flood use so grit does not dry in the housing. Drain the hose downhill, coil the cable loosely, and store the pump dry. Refit the filter basket or strainer before the next job. The Consumer Rights Act 2015 covers goods that are not as described, including residual and plug claims. That is a purchase path, not a reason to keep running a damaged cable.

Common questions

How do I get the last millimetres?
Finish bulk removal in float-auto if you like, then clip or fix the float for continuous run on a hard base with a wide hose. Stay present and unplug as the flow turns to air. Wipe any remaining film by hand.
How do I set the float for continuous run?
Follow the maker’s clip, lock or cable-tie guidance so the float stays in the on position. Improvised ties work on many clear flat pumps. Duals often have a height adjuster or a fixable float. Never leave that defeat engaged on an empty sump.
What hose diameter should I use?
Match the pump outlet, often about 25 mm or the Dual’s multi-size adapters, and avoid a narrow garden hose as the main run. Reviewers who throttle Duals through thin adaptors report real flow far below the headline litres per hour.
Do I need an RCD?
Yes for outdoor and wet-area work. Use a tested RCD-protected supply and press the test button on a sensible schedule. An RCD does not fix a damaged cable. Replace damaged leads, and do not keep resetting a trip you cannot explain.
Why does the pump stop early?
Usually float-auto has reached its cut-off while water remains, or the hose is kinked. Less often the inlet has sealed on the floor or grit has jammed a clean impeller. Check mode and hose before you assume a failure.
Can the inlet seal on the floor?
Yes, especially with bottom suction on soft liners or glass-smooth plastic. Raise the pump on a grid or board and keep the inlet clear. If flow collapses, lift the pump rather than pulling against a stuck liner.
When must I unplug before handling?
Always unplug before lifting, clearing blockages, changing Dual bases, or fishing for a lost hose clip in the water. Sensor probes and float arms are not safe to adjust while the pump is live.

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

Clean vs dirty water submersible pump: which to buy

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)