Mikvaot, Chapter Six, Mishnah Two
1) If a bucket was full of utensils and they were immersed, they become clean;
2) But if [the bucket] was not immersed, the water in the bucket is not considered as joined [with the water of the mikveh] unless it be joined [by means of a hole in the bucket which is as big] as the tube of a water-skin.
Section one: If one fully immerses a bucket into a mikveh, and in the bucket there are vessels that he wishes to purify, the vessels become clean. The waters of the mikveh enter the bucket and therefore even if the mouth of the bucket is narrower than the tube of a water-skin, all of the vessels count as being in the bucket.
Section two: If he didn’t put the entire bucket into the vessel, just part of it, and the waters of the mikveh entered the vessel through a hole in the vessel, then that hole must be as big as the tube of a water-skin. As we have seen, this is the size that allows the waters of the mikveh to be joined with another container.