According to the wiki, there’s a number of different things you can do to raise your Purge meter, but there’s a catch: each of these things you do counts only once during a certain time period. For official servers, this period is 15 minutes.
For example, it doesn’t matter if you kill one NPC or the whole Black Galleon, if you do it within 15 minutes. Likewise, it doesn’t matter if you place one ceiling or build a whole castle within that 15 minute period. But if you kill an NPC and place a ceiling, those count separately.
Even armed with that knowledge, it’s a right pain in the ■■■ to trigger the Purge if you don’t have clanmates to help. Of course, you could resort to leaving your toon logged in overnight and that should help a lot. I don’t do that, because I don’t want to leave my PC running overnight just because Funcom doesn’t wanna give me a way to help grow my Purge meter voluntarily