You're better off plumbing it into the manifold, rather than into the air cleaner if you can. I'd rather coat the inside of my manifold, rather than my carbie.

going a bit off topic,
It's absolutley amazing how much water can collect in a catch can. I was certain I had a blown gasket, or a cracked head. But after doing a leakdown test of the cooling system, and putting a sniffer in the radiator, It's been given a clean bill of health.
I might need a bigger catch can though.