Drain-tanking

Overview
Drain-tanking refers to a Warlock's tactic. It is the process of using Drain Life on your target to keep you alive while damaging the target. In most cases, this is coupled with the heavy use of DoTs on them.

In the 2.0 patch, Drain Life was buffed twice, making this tactic even more appealing. Both its gain from spell damage equipment was drastically increased, and the respective talent (previously Improved Drain Life, afterwards Soul Siphon) grants a lot more damage increase.

In PvE, this is a quite popular tactic among Affliction Warlocks, as it allows the player to fluidly kill mobs. In PvP, it received more attention past 2.0.

How-To
It is important to mention that Fel Concentration is a necessity, as it allows your channel to be maintained.

Generally, the main purpose is to stack all available DoTs on the target (Corruption and Curse of Agony, for Affliction Warlocks additionally Siphon Life and Unstable Affliction). Then the target's life is simply drained. Normally this will keep the Warlock at full health, while relatively quickly killing the target.

It works great in combination with Life Tap. Before engaging battle, you can tap to get full mana. Then, your life will slowly increase, as the gain in most cases is higher than the damage received. Especially with Dark Pact, this effectively allows the player to constantly and quickly kill mobs with little to no downtime.

In time-critical battles, Nightfall can help you a lot, as it procs fairly regularly, providing extra damage.

How to build for Drain-tanking
Talent Requirements
 * 1) Fel Concentration (5) - Allows you to channel drain life while critters are kicking the life out of you.
 * 2) Improved Corruption (5) - extra instant cast DoT
 * 3) Improved Life Tap (2) - boost mana/health cycle
 * 4) Soul Siphon (2) - boosts Life Drain for each dot on the critter
 * 5) Siphon Life (1) - Passive health drain and extra debuff (+4% Life Drain)
 * 6) Shadow Embrace (1) - Adds a free debuff (+4% Life Drain) -- only use one talent point

Talent Recomendations (in order of preference)
 * 1) Shadow Mastery - Makes all shadow damage and Drain/Siphon Life better
 * 2) Demonic Sacrifice - Sacifice Succubus for 15% shadow damage (includes life drain)
 * 3) Demonic Aegis - Boosts Fel Armour
 * 4) Empowered Corruption - +dmg bonus 135% for Corruption
 * 5) Unstable Affliction - Extra DOT for large amounts of damage
 * 6) Improved Curse of Agony - Makes Agony better
 * 7) Nightfall - Instant cast DD (random)
 * 8) Shadowburn - Instant cast DD (this could be considered a waste of 11 points)
 * 9) Demonic Embrace - More sta
 * 10) Fel Stamina - More Health
 * 11) Improved Drain Soul - boost your mana at the end of the fight
 * 12) Dark Pact - Steal Imp's mana at the end of a fight

Drain Tanking example build DP/MF.