One thing to be aware of is that the purge meter will slowly drain while you’re offline. I’ve found that it takes about 2-3 hours of play to counteract this, so unless you’re playing significantly more than that and not missing any days, then it could be very hard for a solo player to counteract.
EDIT: BTW, you might find this post informative if you’re trying to grind your purge meter: What causes the purge to spawn?