A modular assembly for the basement of an animal, in particular pig, breeding building, which basement is intended for the collection and the discharge of liquid and solid waste from said animals, which comprises: - a first part forming a "gutter" for discharging said liquid waste which, viewed from above, is "U"-shaped, the central and transverse portion of which includes an upper face at least part of which is shaped as a recess, this central portion being bordered by two horizontal, parallel and longitudinal wings; - a second part forming a "collector" of the solid waste, which has a generally "U"-shaped section and which comprises a horizontal bottom and two parallel and vertical wings; - a third part forming a "collection pit bottom" for collecting said waste, characterized by the fact that: - the height of the wings of said second part forming collector is greater than the height (h) of the wings of said first part; - said third part has a "U"-shaped section, the bottom of which is flat and provided with a central and longitudinal rib which protrudes on its upper face, and has two parallel and longitudinal wings, the height of these wings gradually increasing from the proximal end to the distal end of this third part; - said third part is bearing on the one hand, on a vertical wing of said second part so that its proximal end is vertically above the bottom of this second part and on the other hand, on the two horizontal wings of said first part, so that its distal end is vertically above said recess-shaped portion and so that when said first and third parts are laid on a flat and horizontal support, the flat bottom of said third part has a downward slope in the direction of said first part. - a first part forming a "gutter" for discharging said liquid waste which, viewed from above, is "U"-shaped, the central and transverse portion of which includes an upper face at least part of which is shaped as a recess, this central portion being bordered by two horizontal, parallel and longitudinal wings; - a second part forming a "collector" of the solid waste, which has a generally "U"-shaped section and which comprises a horizontal bottom and two parallel and vertical wings; - a third part forming a "collection pit bottom" for collecting said waste, characterized by the fact that: - the height of the wings of said second part forming collector is greater than the height (h) of the wings of said first part; - said third part has a "U"-shaped section, the bottom of which is flat and provided with a central and longitudinal rib which protrudes on its upper face, and has two parallel and longitudinal wings, the height of these wings gradually increasing from the proximal end to the distal end of this third part; - said third part is bearing on the one hand, on a vertical wing of said second part so that its proximal end is vertically above the bottom of this second part and on the other hand, on the two horizontal wings of said first part, so that its distal end is vertically above said recess-shaped portion and so that when said first and third parts are laid on a flat and horizontal support, the flat bottom of said third part has a downward slope in the direction of said first part. - the height of the wings of said second part forming collector is greater than the height (h) of the wings of said first part; - said third part has a "U"-shaped section, the bottom of which is flat and provided with a central and longitudinal rib which protrudes on its upper face, and has two parallel and longitudinal wings, the height of these wings gradually increasing from the proximal end to the distal end of this third part; - said third part is bearing on the one hand, on a vertical wing of said second part so that its proximal end is vertically above the bottom of this second part and on the other hand, on the two horizontal wings of said first part, so that its distal end is vertically above said recess-shaped portion and so that when said first and third parts are laid on a flat and horizontal support, the flat bottom of said third part has a downward slope in the direction of said first part.