I purge in about 2 - 3 miles. After I switch, I watch for the temp gauge to go back down to ambient.... I'm sure that it's completely purged by then, because a lot of heat is retained by my brass connections for the sender...
Sounds like you're about to have it whipped!
I've looked for a cross for their filter, haven't found anything yet. You can order them straight from Ramco for a decent price... I still have my original filters on, probably done close to 10K on them... I do have two extras I carry with me though...