a pump down tool includes a resilient cup on the tool exterior to minimize leakage of pumped fluid around the outside of the tool when the tool is pumped into a well . the resilient cup is concave toward an upper end of the tool so it expands upon application of pressure to pump the tool into the well . the resilient cup is capable of expanding to a diameter sealing against the inside of the casing string . a fluid bypass around the resilient cup allows a fraction of the pumped fluid to stir up any proppant lying in the path of the tool thereby allowing the tool to move through a horizontal well without having to plow through the proppant .