do not put a pre filter on those pipes you will have a flood. a sponge polyfiber filter bag at the end of the drain were the water poors into your sump is your best bet. the bags rock but need regular cleaning to keep tip top.
I use to use sponges in filters to catch algae. I never had a problem. Just rinse them thuroughly first. I have also used non bleached coffee filter. The only problem I ever encountered was flow rate. Some sponges did not let the water flow quickly enough.