I’m not finding much info on this achievement (well, none actually). I was going to work on the “filth” section in the Museum, and one of the displays indicates I need it. Anyone able to tell me what it is?
It’s a kill “so many” achievement, most displays require one or more kill achievements to upgrade them. It is, specifically, the top tier evolved filth achievement which is set at 2000.
A good way to farm this and/or shades is get a group and run the wave defence mission at the Kaidan lair, then when the boss arrives, jump over the railing to reset the mission and repeat. 
Which one is that? That the one from the tank guy? Hope it’s not that one…I once paused that mission and can’t get it started again. Am missing that beacon thing and haven’t been able to restart the mission. I keep meaning to send in a petition but keep procrastinating.
No, it’s the one at the lair.
@Pilchenstein
Doing the wave defence is okay if you have a group to do it with. You could also run around inside and combine it with a Komainu kill farm. If you don’t have a group, and want to do it solo, the best option is the Roman Baths in Carpathian Fangs. Start at the filth pool and do a small circle run. Should net you the achievement in no time.
I found that the best way to farm shades was to do the Penthouse. Kill the 4 waves of 4 shades and then /reset before the beasts spawn. 
Neither the penthouse nor the roman baths will get you evolved filth kills.
Hehe, true enough. Shades, on the other hand…