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.