Can you borrow a cat trap? Usually a shelter will have one, but you might have to leave a deposit until you return the cage.

If you can get one, put it near the vent and put sardines in it for bait.

What would you do with it if you can catch it?

I have three cats that I trapped. I had them neutered and immunized and then let them back out into my yard. They are getting much friendlier now that I've been feeding them.

Keep us posted on what you decide to do.

Mary