When you reach Mokumana village, you will have many path options to take. Just to the right of the post office and ball shop, there will be a path that goes down through a rock tunnel. There’s a checkpoint right by this tunnel. Go through it and you will have a waterfall to the right and another rock tunnel to the left. You will take the rock tunnel directly to the left. This will lead you to the base of the waterfall and there will be a post box and sign pointing you down to Slug Garden Meadow. Take the path down. Here you will meet a Slug Gardener who has left his tools and he puts an icon on your map to go retrieve them. Go East to the icon that he placed on your map to retrieve the vacuum. Once you have retrieved the vacuum, you will need to actually suck up a slug for the achievement to pop. Slugs are the small, purple grubs that you’ve been popping all along this path. As you approach one, the camera will slow down and you can hold either LT or RT to suck in the slug and get the achievement.