Abstract: A method and apparatus for removing downhole well debris involves an elongate string operable to pump the debris from a well into the string. A pumping portion of the string includes a hollow piston with a hollow, splined piston rod fixed to the upper portion of the string, above the pumping portion, and keyed to the pumping portion to transmit rotary motion from the upper portion to the debris retaining portion below the pumping portion. A hollow piston head includes a valve, advantageously a ball valve, to prevent downward fluid flow. By reciprocating the upper portion, well debris is pumped into the debris retaining portion and solid debris is trapped therein by a one-way check valve. The liquid debris, such as heavy water, continues upwardly through the string passing through the interior of the piston and into the upper portion.