Water PRE filtration. Before it goes into your filter. Anyone thought of or tried this?

[HBARleatherneck]

Bubble bags. Evidently they are for making dope. I saw them in the farm and garden section of craigslist and looked them up on amazon. Now, I know you could use a t-shirt, cheese cloth, just about any fabric for less money. I like the idea of a dedicated item for the job. Plus different microns of filtration between the bags. And set up for 5 gallon buckets.
http://www.amazon.com/iPower-GLBBAG5...ds=bubble+bags

8 bags for $43 doesnt seem bad.

What do you guys think? I had no idea they were for anything nefarious.