1. IN A DISCHANGE SYSTEM FOR MATERIAL CARRYING TUBES, AN ELONGATED MATERIAL CARRYING TUBE HAVING A DISCHARGE OPENING FORMED IN ONE PORTION THEREOF, A CLOSURE TUBE MOUNTED IN SURROUNDING RELATION TO SAID CARRYING TUBE AND COMPLETELY ENCLOSING THE PORTION OF THE CARRYING TUBE POSITIONED WITHIN SAID CLOSURE TUBE, MEANS FOR RECIPROCATING SAID CLOSURE TUBE WITH RELATION TO SAID CARRYING TUBE TO AND FROM ONE POSITION OVERLYING AND CLOSING SAID OPENING AND A POSITION SPACED THEREFROM TO ALLOW DISCHARGE FROM SAID OPENING, BOTH OF SAID SEAL MEANS BEING SPACED OPENING AND SECOND SEAL MEANS POSITIONED ON SAID OTHER SIDE OF SAID OPENING, BOTH OF SAID SEAL MEANS BEING SPACED LONGITUDINALLY FROM OPPOSITE BOUNDARY EDGES OF SAID OPENING TO THEREBY PROVIDE A SPACE BETWEEN THE OPPOSITE BOUNDARY EDGES OF SAID OPENING AND EACH SEAL MEANS, SAID FIRST SEAL MEANS BEING CARRIED BY SAID CLOSURE TUBE AND HAVING A SLIDING, SEALING ENGAGEMENT WITH THE EXTERIOR WALL OF SAID CARRYING TUBE COMPLETELY AROUND SAID CARRYING TUBE TO FORM A FLUID TIGHT SEAL WITH SAID TUBE, SAID SECOND SEAL MEANS BEING POSITIONED ON THE OTHER SIDE OF SAID OPENING AND COMPRISING A RESILIENT SEALING RING SURROUNDING ONE OF SAID TUBES AND FIXED THERETO, AN ANNULAR SURFACE CARRIED BY THE OTHER OF SAID TUBE IS IN SAID TO SAID RING AND COOPERABLE THEREWITH TO SEAL SAID OPENING IN FLUID TIGHT RELATION WHEN SAID CLOSURE TUBE IS IN SAID OVERLYING POSITION, AND MEANS FOR SUPPORTING SAID CLOSURE TUBE ON SAID CARRYING TUBE INCLUDING A PLURALITY OF ELONGATED RODS AND GUIDES ON SAID CLOSURE TUBE IN SLIDABLE ENGAGEMENT WITH SAID RODS, SAID RODS BEING SUPPORTED BY BRACKET MEANS ON SAID CARRYING TUBE AT POINTS SPACED LONGITUDINALLY OF SAID OPENING AND SAID CLOSURE TUBE.