Drain ability help

Drain ability help

I need help with a drain ability.
How do I make it so it drains mana from the target unit, but does not give it to the caster?

That's easy, and you don't need the Siphon Mana skill! Just search the Mind Rot ability, it consumes mana every sec without give it to the hero.
If you like to make a channeling drain, use the Siphon Mana skill, now reduce the 'Mana factor bonus' (My english isn't perfect) to 0, set the numbers to Drain in 'Mana consumed per sec'