Afsal,
Pushing water through it is better. But that normally means you have to put it inside bags/in betwene sponges or something similar, which then implies more maintenance IMO as you have to clean it because detritus gets trapped in sponges/bags etc.
Mine are in bags/socks, and in a high flow area, but the water does not get pushed through it so no detritus gets trapped. But this would be less efficient.