The mounting bracket for your new garbage disposer assembles by inserting the fiber gasket, back-up flange and mounting ring over the sink flange, in that order. Be sure to hold these three pieces in place while you insert the snap ring over the flange. It’s called a snap ring because you’ll hear it snap in place. Then firmly tighten the three mounting screws against the backup flange, being careful to tighten them evenly.
Another common cause for a leaking garbage disposal is the disposal flange. A leak at the very most upper area of the garbage disposal could be the garbage disposal flange which goes through the sink. A garbage disposal flange should be sealed with Plumber’s putty and then tightened from underneath the sink. If this is not tight enough or if it has managed to come loose (which can happen) then the garbage disposal will have to be taken down so the flange can be resealed and then the garbage disposal can be rehung.