Planet Tideline Overflow Help

[Clownfish2]

I’m planning to plumb a Planet Tideline 20 inch overflow. The rubber gaskets have a smooth flush side and a Ribbed side. Which side (smooth or ribbed) mounts against the back panel of my aquarium?

Thanks

 

[Tumey]

A phone call to Planet Aquariums directly would confirm installation positioning but based off their pic you’ve posted it appears the rib side gets installed facing the glass.

 

[Cell]

Smooth side should be against glass and ribbed on the nut side.