Kessel Aqualift S Basic Instructions De Pose Et D'utilisation page 28

7.3 Backflow preventer
CAUTION
Accumulated wastewater flows out!
Open the turn fastener.
Pull out the non-return flap.
Clean the non-return flap.
Check the components for wear and reassemble in
reverse order.
Check tank for heavy soiling, clean if necessary.
Do not use pointed objects.
Maintenance is completed.
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