Rinsing them in bleach would most likely harm them, and would definately harm your fish, even in a tiny amount, if any remained on the plant.
Warm water usually gets rid of any foreign particles, don't use scalding hot as it'll hurt the plants.
The 'parasites' your friend means are probably snails - almost every planted tank has them. Picking them off when you get the plants and maybe using a snail-rid soak BEFORE you put plants in the tank, then thoroughly rinsing will stop them invading.