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Rainwater Underground Cisterns

Underground Cistern
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Graf Carat Underground Cistern is available in sizes from 700 to 1700 gallons. Ideal for Rainwater or Grey Water Retention. Standard Pedestrian Manway, 14" Telescopic Riser and Childproof PE Lid.

Easy and safe assembly

The patented quick connection (illustrated in green), allows the Carat tank to be assembled without screws in only few minutes. Disassembly is possible at any time.


Variable burial depth: 30" to 42" (59" Max. w/optional dome extension )

(w/additonal telescopic cast iron manway kit)

Groundwater stable to middle of the tank due to extremely rigid construction

15-year warranty

Made from high quality Duralene; easy to recycle

Can be expanded as required

26" Manway opening


The first-class EPDM material used in the profile seals (illustrated in yellow), has been laboratory tested to last more than 25 years.

The centering bolt (illustrated in orange) assures the accurate and easy assembly of the two half shells preventing any leaks.

Flush with ground level (2 seals) The GRAF Carat S underground tank has numerous seals to effectively stop dirt getting into the tank.

This means that seepage water cannot get into the tank and, thus, dirt particles cannot contaminate the rainwater. The seals are in the intersection between the tank and the tank dome and between the tank dome and the telescopic dome shaft.

All supply pipes connected to the tank dome are also sealed with five lip seals as standard.

Frost-proof installation underground

Groundwater stable up to the middle of the tank due to extremely rigid construction


The GRAF Carat S underground tank has a rotating tank dome. The tank dome can be aligned with the connections independently of the tank – this makes installation much easier.

All installation pipes are connected using the five standard lip seals. The Carat S telescopic dome shaft connects the system to the ground surface. The height of the tank can be smoothly adjusted to suit the local conditions and it can be tilted by 5°. The whole system is flush with ground level.


4 Item(s)

4 Item(s)