grey/black water tanks - how to attach

Please excuse another rookie question. How do you attach the grey/black water tanks to the frame/deck?
I've seen tanks that have flanges and some that don't. For the flanged tanks, I assume you screw/bolt them to the bottom of the trailer frame/deck. For the non-flanged models, I assume you use strapping or bolts and Uni-strut.
Thank you for your replies.
I've seen tanks that have flanges and some that don't. For the flanged tanks, I assume you screw/bolt them to the bottom of the trailer frame/deck. For the non-flanged models, I assume you use strapping or bolts and Uni-strut.
Thank you for your replies.