Abstract: A collector bag for a catheter comprising a first receptacle and second receptacle selectively fastenable to each other. The first receptacle, serving as a temporary reservoir for fluids while the second receptacle is detached for disposal of its contents. The first has a top end with a throughbore forming a catheter attachment port while the bottom end incorporates a valve movable between an open and closed position thereby controlling the flow of fluids therebetween. The second receptacle serves as the primary receptacle for collecting fluids with a collar serving as receiver for the first receptacle bottom end that once inserted rotation of one member relative to the other in a predetermined direction locks the two receptacle together. Once fastened thereto, the valve can be opened to provide for fluid passage between the first and second receptacle.