Bring 4 boxes of TNT (I only brought 3, but still managed -- I had to kill one of the tanks with regular crossbow shots while ducking in and out of a safe room). Enter in your stealth suit, don't turn on your shield yet. After the Mouth of Tchort gives his little spiel, stealth IMMEDIATELY and head to the right area. Plant a TNT next to the upper right tank, then head to the lower right one. After the boom, every enemy will move to investigate, that's your cue to drop the TNT on the lower right tank. The next part will be a bit tough, but essentially you want to cross all the way to the left and enter the little shack without getting attacked, while wearing at least a gas mask (otherwise the gas will hurt you bad, and you definitely don't want the +damage debuff on you at any point). Once there, close the door behind you to drop any suspicion for enemies, then head to one of the mutagen tanks on the left in stealth, drop TNT, run back to the room, close the door. Wait a few seconds so that enemies move to investigate the explosion, then the coast should be clear to go to the other tank, drop another bomb, and then run like hell (still stealthed!) to the safe room near the ladder you entered through. Enter the room, close door behind you, equip fire/shock bolts and fire grenades as well as your preferred combat suit (acid/bio resistance preferred, as well as high movement... I just used my stealth suit for this).
For the next bit, I suggest popamoling the nearest tentacle (break LOS by hiding in the house) and killing all the tchortlings that come visit (you can pre-trap the pathways to make this MUCH easier). Once at least one tentacle is dead, rush up to Tchort (don't forget to keep dropping quick tinkered bear traps on the path behind you to catch respawning 'lings), kill any tentacles that are alive... focus the thought control (psi) one first, because bilocation will fuck you up. After 3 tentacles are dead, you can just murder tchort with Aimed Shot, maxed shock bolts, and poison (if you have hypertox). With all 4 mutagen tanks destroyed, it takes a LONG time for them to respawn.
Oh yeah, it's probably obvious, but keep in mind that you can just exit combat if enemies can't get to you for 4+ turns. This'll give you an opportunity to freely re-equip, heal, recharge your NVG, re-stealth, etc. Also, DO use NVG during the shooty parts, otherwise your accuracy will suck.