A pump adaptor for on-the-go reducing the size of an inlet end of a utility pump having a static immersible one-way valve on an inlet end with the pump adaptor having a constricting band for forming a sealing surface with a portion of a pump barrel located downstream to the immersible one-way valve with the adaptor including a chamber for a static immersible one-way valve to enable reduction in the inlet to the utility pump without reducing the pump stroke capacity and without affecting the normal operation of the static one-way immersible valve.