We have a spigot at the back of our house that leaks horribly through the anti-siphon cap on top. I did some Googling and saw several references to getting replacement part kits to fix it.

I have a feeling this is a dumb question, but is this an operation that requires shutting off the water (to the entire house, since there's no separate valve for that connection)? I generally shut off the water any time I'm doing anything plumbing-related, just for safety. But it can be a real hassle. And since water doesn't come out of the anti-siphon cap when the faucet is off, I'm wondering if the whole assembly is on the outside of the faucet valve, and can be removed "hot." Is this possible? Is it foolish?

Any other tips for this repair?

Thanks.