What size Buchner funnel?
It does not really matter, of course you want to be able to evenly spread it out. however, i would recommend a 12.5 cm, "that will do the job".
by having a big one and less product it will spread and stick to the paper all over, by having a smaller one it helps you keep all the yummy product all togeather.
12.5 will be suficiant"""cm that is..."
Also be carefull what questions you post on the hive" as this may be considered as crap. MAKE SURE you search not just on the hive but else where. Look on google and see what size funnel they use in the pracs or what the overall size is that people are using in online pracs.
clearly you have limited knowledge, read read my friend as i was told and please use the search engines available on the HIVE and WEB..."