If a tormenter spawns stop hiding behind the ADU, you're just make the tormenter attack it. If you run away from it while shooting the tormenter it will follow you, so instead of leading in to the ADU lead it away.
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Having one person on the tormentor helps (and lead away) as the other 2 can make sure the rounds done... the adds will stop spawning and the tormentor can be dealt with properly (if not already). Having people blast through spawns works well for 4/5 of it... but last set involves a lot of teleporting adds; roaming supers are fine, but caution needed. I've failed a few 40's by tethering spawn but they all move on top of the adu; had I waited then I could have tethered everything. Defense upgrades is an interesting situation; horses for courses!