Did take the 1/2" bit and drilled 3 holes into the narrow part of the keel behind the sump. Went in an inch and a half each and got only green/white tailings out of the holes. Drilled into the lower part under where the propeller shaft would go if 338 had one. The area is stepped and sloped to get bilgewater to drain to the sump at the end of the ballast under the companionway. Given the narrowness of the area, there is very little volume in the buildups.

I looks like the fill is solid plastic and glass. Which is stronger and gooder. I'ld rather have that there than bloody foam!