go check ur sink facuet(sp) unscrew the nozzle where the water comes out and low and behold there should be a screen but if not i've seen crack heads use steel wool for a screen they just take a chunk and throw it in their pipe
and only if you don't have either and can't go get a screen from someone else or go blaze with someone whos got a screen i guess u could use tinfoil:S not the best thing but for a last choice and u gotta get high i'd use the tinfoil atleast ur gettin high