Depending on the pump alot of guys are using the most coarse scrub pad they can find, or gutter guard. The best scrub pad I found is at Wal-Mart in the cleaning section. It has a white handle glued to it, and is way to thick to use until you fillet it down a bit.
The gutter guard is in the gutter section at Lowe's or Home Depot. I do have a pic of that.