Filter Flask is self explanatory and used for filtration. It is usually made of heavy glass to withstand high vacuum. Back in time, when I was starting, I decided to go cheap and though that I can simply use Erlenmeyer flask with added hose connector to vacuum my liquid. My lesson learned - 6 hours of cleaning imploded glass and material from the laboratory floor and wasted glass and labour. Do not cut corners on Filter Flask, never use anything else but specially build filter flasks. Normally we sell Simax EU made from Pyrex glass and Pyrex by Corning filter flasks available in multiple sizes, which complement our Buchner funnels.