basic question about aattaching surface skimmer box

[fishgate]

I am about to drill and attach my surface skimmer (overflow) box (4 sided). Do I put the bulkhead gasket between the back of the aquarium and the skimmer box? Do I just use one gasket?

 

[zachts]

you'll need two if the flange is on the inside of the tank. one on the flange inside the box and one between the box and wall of the tank.

with flange outside the tank you'd only need the gasket outside the tank on the flange.