I say, and with God's success: If a mouse, or a bird, or something similar dies in the well, it should be examined: if the object that fell into the water has swollen, then all the water of the well must be drawn out. However, if it has not swollen, then it is obligatory to draw out from the well 20 buckets, and it is recommended to draw out up to 30 buckets, and this should be done after removing the object that fell in. The standard for the bucket is the medium bucket, and anything larger than that is counted. If the obligatory amount is drawn with a large bucket, that suffices for achieving the goal. Refer to: Al-Ikhtiyar 1: 26, Al-Wiqayah p. 102, Al-Maraqi 37-38, Al-Bahr 1: 124, Al-Badai 1: 86, and God knows best.