Viega 6161.52 Instructions For Use Manual page 13

Handling
Fit profile seal in the overflow unit.
If the wall thickness a in steel bathtubs is less than 3 mm, insert
addition seal for steel bathtubs between profile seal and bathtub.
Push the rubber sleeve onto the overflow unit pipe until the lower
edge is flush with the edge of the overflow pipe.
Fit inlet flange into the overflow unit.
Screw in fixing screw and tighten hand tight.
On the hexagon of the mounting aid, there is a groove, which must
be positioned on the lip of the fixing screw.
Multiplex Trio drain/overflow functional unit 13 from 20