Then fill the bottom with trub, to just below the holes.
Now snap on the lid and place your trap in your garden.
Here is one guarding my strawberry patch. The lid keeps out the rain and any curious pets. There is no need to refill very often. The trub will keep luring slugs for a good long time. If you don't have coffee containers, large yogurt tubs work equally well.
While I was in a trap making mood, I used an empty sour cream tub to make a similar lure for my ants, using my favorite formula (shared in an earlier post). I plan to make many of these and leave them in the rooms whenever I spot an ant.I'll let you know if they work.