A valve unit for regulating a flow and a disposable urine bag are provided. The valve unit includes an inlet portion and an outlet portion separated from each other by a slide valve. The slide valve includes a female part in direct communication with the inlet portion and the outlet portion and a male part axially displaceable in liquid-proof contact with the female part. The male part includes a closing position wherein a portion of the male part is outside the female part and an open position wherein the male part allows liquid passage between the inlet portion and the outlet portion by means of a communication part. The female part includes a tubular member open at both ends and having a tubular wall extending along the entire length of the male part in the open position for deterring displacement of the male part to the closed position.