An improvement in a pipe flushing device is provided. The device includes a hollow, elastomeric tubular member expandible by water pressure and having open opposite ends. A hose connector is connected to the inlet end thereof and a valve connected to a transverse groove in the outlet end thereof. The valve includes a hollow cylindrical cage with open sides and front and a rear transverse closure plate sealing the rear end thereof. The plate may have a peripheral flange and in any event seats in the transverse groove. An elastomeric sheath which is both flexible and resilient forms the improvement. The sheath removably covers the exterior of the rear closure plate and helps seal the valve in the groove to prevent fluid by-pass except when the tubular member is expanded. The sheath may have a roughened slip-resistant exterior surface or striations in the exterior thereof to improve the seal and may enclose a portion of the sides of the cage. Alternatively, the sheath can cover the whole valve except the open front thereof and in such instance has perforations in the cage side-covering portion to allow water access to the interior of the cage. The sheath and valve cage form an improved valve assembly.