From wow.incgamers.com

Statistics

Talent Improvements

The talents listed below affect Drain Mana in the following way.

Affliction Tree

Talent: Suppression
Effect: Reduces chance enemies resist Affliction spells.
Statistics: Rank 1 = -2% chance, Rank 2 = -4%, Rank 3 = -6%, Rank 4 = -8%, Rank 5 = - 10%

Talent: Grim Reach
Effect: Increases range of Affliction spells.
Statistics: Rank 1 = 10% increase, Rank 2 = 20%.

Talent: Soul Siphon
Effect: Increases amount drained for each Affliction effect on the target, up to a maximum % additional effect.
Statistics: Rank 1 = +2% drained (max 24%), Rank 2 = +5% (max 60%).

Talent: Improved Drain Soul
Effect: Returns mana if target is killed by you while you drain its soul. Also, Affliction spells generate less threat.
Statistics: 1 point = returns 7% mana & 5% less threat. 2 points = returns 15% mana with 10% less threat.

Talent: Contagion
Effect: Increases the damage of Curse of Agony, Corruption and Seed of Corruption and reduces the chance Affliction spells will be dispelled.
Statistics: 1 point = +1% damage & -6% chance skill is dispelled, 2 points = +2% & -12%, 3 points = +3% & -18%, 4 points = +4% & -24%, 5 points = +5% & -30%

Demonology Tree

Talent: Mana Feed
Effect: When you gain mana from Drain Mana or Life Tap spells, your pet gains % of mana you gain.
Statistics: Rank 1 = +33%. Rank 2 = +66%. Rank 3 = +100%.

Threat Level

Details of threat level generated by Drain Mana.

Uses in PvP

Please feel free to add a bullet list of uses within PvP or editorial if you have more to say. What use is it against other builds, what skills can it be used to counteract or prevent. What skills does it work well in combination with.

Uses in PvE

Please feel free to add a bullet list of uses within PvE or editorial if you have more to say. Which creatures/bosses in particular is it useful against.

Facts about Drain Mana

• Channeling spell.
• Needs 3 seconds of channeling before mana used to cast is gained back.