Drain ability help

[martix]

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?

 

[Arcsol]

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'