An ostomy receiving bag includes front and rear walls sealed along a rim of the bag and a cover sheet attached to the bag. The bag has a lateral midline located between an upper end of the bag and a bottom end of the bag, with an inlet opening nearer to the upper end than to the bottom end of the bag. The cover sheet is attached to the upper end of the bag at the rim and covers at least part of one of the walls to form a pocket and an unattached edge between the upper end of the bag and the bottom end of the bag. A collecting volume of the bag is reduced by at least 25% when the bottom end of the bag is placed under the cover sheet to a position between the lateral midline and the upper end of the bag.