This is how I top crop yeast from a carboy. My sanitized blowoff tube feeds into a sanitized 2 quart jar with a lid fitted with 2 bungs. One bung for the out end of the blowoff tube, the other for an airlock. I discard the brown yeast that comes out first and keep the rest. The part of the blowoff on the carboy end is fitted with a shortened racking cane so I can get down near the surface of the fermenting beer and collect what I need for the next batch. Sorry no pictures. Hope my description is sufficient.