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Carat XL underground tank retention cistern

The GRAF Retention cistern combines rain retention with rainwater harvesting.

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Carat XL retention cistern

The GRAF retention cistern is a combination of rainwater retention and rainwater harvesting. The detention can be larger if required. In this case, part of the rainwater can also be used in addition to the required detention volume. For example, rainwater can be used for the following applications:

• Watering gardens

• Flushing toilets

• Washing machines

• Cleaning

The use of rainwater means that up to 50 % of drinking water can be saved, and up to 85 % for commercial properties.

The retention cistern is designed such that the rainwater first fills the useage volume. When the useful volume is full, the throttled outflow is activated and the detention volume also becomes available for temporary storage. The detention mechanism with throttled outflow in turn corresponds to a conventional retention system. Following the rainfall event, the position of the outflow prevents the detention cistern from being completely emptied, while the useage volume remains in the tank!

Advantages Carat XL retention cistern:

  • Suitable for HGV loading up to 12 t
  • Dome opening with stainless steel profile for precision fit and secure mounting
  • Can be mounted in groundwater
  • Lower weight than concrete and steel
  • Various connection surfaces DN 100 (4") / 150 (6")
  • Investment security thanks to a 15 year warranty











8,500 l

order no.Length (mm)Width (mm)Height (mm)Inner Ø dome shaft (mm)add to enquiry
Weight (kg)

10,000 l

order no.Length (mm)Width (mm)Height (mm)Inner Ø dome shaft (mm)add to enquiry
Weight (kg)

Technical details

max. earth covering (mm) (without groundwater, vehicle loading)max. axle load (t)max. vehicle weight (t)
200083,5 t / 12 t
Earth covering with loading capacity (mm)Earth covering with groundwater installation (mm)
800 - 2000500 - 1800


Mini telescopic dome shaft with lid, suitable for pedestrian loading


Maxi telescopic dome shaft with lid, suitable for pedestrian loading


Telescopic dome shaft with cast iron lid, suitable for vehicle loading


Telescopic dome shaft TRUCK

Telescopic dome shaft TRUCK for concrete rings


Choke drain package detention/retention

For underground tank Carat 0,05 - 2,0 l/s, DN 100 connection, 3 m hose


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