4.
T
ANK
INS
TALLA
TION
Graf UK Ltd
7
Insertion and filling
The tanks must be inserted, impact-free, into the
prepared trench using suitable equipment. The tank is
filled with 1/3 water before starting to backfill.
Afterwards the surrounding (roundgrain gravel,
max. grain size 10 to 20mm) is then filled in layers of
max. 30 cm steps and is compacted. The individual
layers should be manually tampered to ensure no
voids. Damage to the tank must be avoided during
compaction. Mechanical compaction machines must
not be used under any circumstances. The surrounding
must be at least 500mm wide.
Ventilation and bleeding
Poor venting and the lack of a Soil Vent Pipe is the
number one cause of smells from treatment plants. All
tanks must be ventilated and bled back through the
soil vent pipe (chimney effect). Air Admittance Valves
(Durgo Valves) must not be used instead of the SVP.
These valves are fine for houses connected to mains
drainage but NOT for ones with a treatment plant.
4
TANK INSTALLATION
Bleeding with a free outflow
Bleeding with percolation or an
obstructed outflow
1. 1/3
2. 3/3
500
