I just puristed slime pits as a Goblin Assassin. Took two tries (well, three, but one of them I thought I'd try the new GG and forgot he doesn't like poison), first one I was *one hit* from beating Meatman. Second one I think I had another level up in me and a badge of courage death protection to spare (2nd post level 10 - I got weytwut early and Binlor->TT and the gold subdungeon, so got two +XP upgrades *and* to convert everything from the shops) in me just about. Unfortunately the random mooks were zombies - you're really hoping to get gorgons or something like that instead just because Slime has so little stuff a purist character (i.e. w/o venom ward, fortitude or burn potions prepped - and you'll probably want to get schadenfreude from the shop for an extra 80 damage on a boss) can afford to hit.
Anyway, it's not easy but given I got one victory and one near-victory run I think GA (or another assassin, goblins are great for purist though since you don't really have the prep power to catapult as much) would be pretty easy with preps.