Otto Graf GmbH
Plastic Products
Tel. +49 7641 589-0
Fax +49 7641 589-50
Carl-Zeiss-Straße 2-6
DE-79331 Teningen, Germany

Carat S retention cistern

The GRAF Retention cistern combines rain retention with rainwater harvesting.

Sizing form/
Tender file
Carat S retention cistern

To guarantee retention of rainwater, a delayed drain is fitted in the channel with 0.05 to 2.0 l/sec. depending on the customer’s specifications and the retention or harvest volumes. In the event of heavy rainfall, the water level in the cistern rises above the max. water level (short term) and is drained into the channel at delayed speed using a floating drain choke.
This relieves the channel and the treatment works.
The water level can rise to the emergency overflow and sinks slowly back down again after the rain to the long-term max. water level. This rainwater can then be harvested.

We also construct and supply individual, special solutions.
Sizes between 3,750 – 100,000 l with corresponding retention volumes are possible.

This special type of rainwater harvesting is prescribed or subsidised in many communities. 

  • For rainwater retention
  • For rainwater harvesting in the house and garden
  • For frost-proof installation in the ground
  • The entire tank volume can be used for rainwater retention
  • "USA Patent 7854338"



3,750 l

order no.Length (mm)Width (mm)Height (mm)Inner Ø dome shaft (mm)add to enquiry
Total volume (l)Retention volume (l)Useable volume (l)

4,800 l

order no.Length (mm)Width (mm)Height (mm)Inner Ø dome shaft (mm)add to enquiry
Weight (kg)Total volume (l)Retention volume (l)Useable volume (l)

6,500 l

order no.Length (mm)Width (mm)Height (mm)Inner Ø dome shaft (mm)add to enquiry
Weight (kg)Total volume (l)Retention volume (l)Useable volume (l)

Technical details

max. earth covering (mm) (without groundwater, vehicle loading)max. axle load (t)max. vehicle weight (t)
200083,5 / 12
Earth covering with loading capacity (mm)Earth covering with groundwater installation (mm)
800 - 2000800 - 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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