It's not. The Tulpa is a unit of thought in your mind given form: if you don't want your Tulpa around any more, than diliberately starving it of attention will make the creature dissolve.
That's just it though: I don't think I could do that to what I perceive as a sentient being. That just seems cruel to do to it. So I want to be sure I can stick with it before I do it.