I have seen some posts where they put the lids on the buckets and cut them in half. That way you will have 40 half buckets. A half bucket which will be all you need when using pallet wood sticks most of the time. You will need to figure how much concrete to use then to sink these buckets. PVC is not hardly buoyant as wood and bamboo is very buoyant as it has air chambers between each bamboo joint. There fore you would need way more weight to sink bamboo than wood or PVC. Hard woods are heavier than light woods also so the heavy woods take less extra weight to sink it. Fish habitat" Build it and they will come"