Help! I'm need to replace my bulkhead on running dt

[Lifer]

I'm trying to get my existing bulkhead nut off on a already up and running tank. I drained the overflow and I can't get the nut off of the bulkhead fitting. Everytime I try to turn it the bulkhead turns too! I need to get the bulkhead out and replace it ASAP! Any suggestions

 

[Smo]

Can you hold it with channel locks while you turn the nut? Alternatively, hold it with a piece of pipe from the inside.