Never occurred to me that there was a proper orientation.
In any case, use some kind of gasket sealant on both sides as those gaskets often refuse to seal 100%.

SJ

 

if its the tin compression ones you are on about,chuck em away and get the thick card ones,or make your own out of some thick card and put a smear of non setting sealant like hylomar blue etc. had many a problem with the tin ones leaking!!!!

 

Yes, ridge side uppermost in the bottom of the bin.

Make your own from gasket paper or a cornflake packet, smear a little grease on both sides before fitting.

Dave.