Get a plastic hammer and "peck" all over your deck, listening to the different sounds of solid areas and soft areas, the tone difference is immediately recognizable. Then map out your soft area with straight lines and square corners. Then set your skill saw to about a 1/4 inch depth and cut out the soft spot. Lift, pull, pry out the top layer. Clean out all rotted stuff, (and good core in the cutout space), saturate the area with cpes. Replace removed core with appropriate sized material, preferably nidacore, klegecell, or even a good marine plywood. Soak again with cpes and fill all voids with thickend epoxy and put your (now cleaned up) top plug back in place befor everything sets up. It sounds a lot more difficult than it is. Drilling holes and suckin on it won't work, been there, done that.