A substance processing receptacle (300, 400, 500, 500A, 600, 700) including a selectively closeable drain connector (100, 800) and a material processing bag (491, 591, 591A, 601, 701) comprising an inner bag surface (492,592,592A) and an outer bag surface, the drain connector (100, 800) comprising: a plunger (110, 210,810) including a plunger body (115, 215, 815) having a first closed end (111, 211, 811), a second open end (112, 212, 812), a wall (120, 220, 820) with an exterior surface (121, 221, 821) and with an interior surface (122, 222, 822) bounding a hollow core (125, 225, 825), and a first and a second circumferential sealing element (133, 134, 235, 236) disposed along the exterior surface (121, 221, 821), the plunger body (115, 215, 815) further defining at least one passage (126A-126C, 226A-226D, 826A-826C) extending from the exterior surface (121, 221, 821) into the hollow core (125, 225, 825) and disposed between the first and the second circumferential sealing element (133, 134, 235, 236); and a drain flange (150, 150A, 250, 850) defining an aperture (165, 265, 865) adapted to receive the plunger (110, 210, 810), the aperture (165, 265, 865) being bounded by an inner surface (166, 266, 866) adapted to sealingly engage the first and the second circumferential sealing element (133, 134, 235, 236) when the drain connector (100, 800) is in a closed state, and to sealingly engage the second circumferential sealing element (134, 236) when the drain connector (100, 800) is in an open state; wherein any of the plunger (110, 210, 810) and the drain flange (150, 150A, 250, 850) is adapted to move relative to the other; and wherein the drain flange (150, 150A, 250, 850) has a radially extending flange lip (151, 151A, 251, 851) with a lower surface (153, 153A, 253, 853) of the flange lip (151, 151A, 251, 851) contacting and sealingly engaged to the inner bag surface (492,592,592A) of a bottom wall (606, 706) of said bag (491, 591, 591A, 601, 701), and the first closed end (111, 211, 811) of the plunger (110, 210, 810) is disposed flush with an upper surface (152, 152A, 252, 852) of said radially extending flange lip (151, 151A, 251, 851) when said drain connector (100, 800) is in a closed state. a plunger (110, 210,810) including a plunger body (115, 215, 815) having a first closed end (111, 211, 811), a second open end (112, 212, 812), a wall (120, 220, 820) with an exterior surface (121, 221, 821) and with an interior surface (122, 222, 822) bounding a hollow core (125, 225, 825), and a first and a second circumferential sealing element (133, 134, 235, 236) disposed along the exterior surface (121, 221, 821), the plunger body (115, 215, 815) further defining at least one passage (126A-126C, 226A-226D, 826A-826C) extending from the exterior surface (121, 221, 821) into the hollow core (125, 225, 825) and disposed between the first and the second circumferential sealing element (133, 134, 235, 236); and a drain flange (150, 150A, 250, 850) defining an aperture (165, 265, 865) adapted to receive the plunger (110, 210, 810), the aperture (165, 265, 865) being bounded by an inner surface (166, 266, 866) adapted to sealingly engage the first and the second circumferential sealing element (133, 134, 235, 236) when the drain connector (100, 800) is in a closed state, and to sealingly engage the second circumferential sealing element (134, 236) when the drain connector (100, 800) is in an open state; wherein any of the plunger (110, 210, 810) and the drain flange (150, 150A, 250, 850) is adapted to move relative to the other; and wherein the drain flange (150, 150A, 250, 850) has a radially extending flange lip (151, 151A, 251, 851) with a lower surface (153, 153A, 253, 853) of the flange lip (151, 151A, 251, 851) contacting and sealingly engaged to the inner bag surface (492,592,592A) of a bottom wall (606, 706) of said bag (491, 591, 591A, 601, 701), and the first closed end (111, 211, 811) of the plunger (110, 210, 810) is disposed flush with an upper surface (152, 152A, 252, 852) of said radially extending flange lip (151, 151A, 251, 851) when said drain connector (100, 800) is in a closed state.