You should clean a party pump after every use - not just to make it work easier, but leaving any beer in the line will lead to bacteria growth. Always make sure a party pump is clean before using on a fresh keg.
You can simply rinse in hot water. Open the fuacet and run hot water from the bottom of the keg coupler and allow it to drain out the faucet.
For a thorough cleaning try one of our pressurized kits:
http://www.micromatic.com/product.php?pid=M5-801147
Use a cleaner developed for the beer industry:
http://www.micromatic.com/product.php?pid=CFP-1
And then re-lube the party pump with probe lubricant:
http://www.micromatic.com/product.php?pid=FT101L
Mike Godwin, Micro Matic USA, Inc. Northridge, CA