I bought one of those inexpensive plastic dust-separator lids for a 30- gallon trash can, but it fit so loosely, the lid lifted any time one of the collector’s 4" hoses moved.

Here's a solution I found hanging in my garage: an old 26" bicycle wheel without its spokes. Mount the bike rim to the lid by passing bolts through 6" springs and the rim's spoke holes, as shown. Slip the other ends of the springs over J-hooks attached to the can, as shown. The springs provide holding power, but release quickly for easy emptying.
—Lee Nye, Naperville, Ill.