Fuel tank leak?

Hello fellow boaters, I Have a question. I believe I have a fuel tank leak, the tank is underfloor mounted. How can I test it for leaks without removing the whole tank? Is there anyway to pressure test it? The boat is about 12 years old and has an alum. tank. How common is it for an alum. tank to start leaking? I have started the replacement of the floor, but the tank is mounted under the bowrider glass section, and Im not sure how it will come out? Has anyone had this problem before.
Thank you in advance for your help.

Not knowing "how" you deternined there's a leak makes it difficult to comment.
Is there constant fuel odor coming from the tank area?
Is there run off in the bilge area?
Does the gauge drop down after a period of time in the driveway?
Have you checked all rubber lines to ensure "they" are not leaking?
How about leakage around the fuel pump itself possibly?
Check all other possibilities and everything that deals with the fuel before you go tearing up your deck, because the hard part is getting it all back in properly without professional help. You wouldn't want a new tank banging around in the rough with the family onboard.
Good luck with your project and hopefully it's just a hose.....

Thanks for the response Stingray.
I noticed some gas in the ski locker, aft of the tank, and forward of the engine compartment. I verified all the hoses were secure. Sending unit, vent, fill, etc. I have started tearing the old floor out, but the only way to get it out is to lift the front bowrider cap section. Dammmm. Some say I can pressure test, and some say not to? If I did, how would I totally seal the vent, fill lines?
Thank you again for your response.
IP:

I too had a bad experience with what I thought was a leaking tank on a older boat. As a last resort I pulled the fill hose all the way out and inspected it. Found the leaks in the hose about 2 ft. away from where it connected to the tank. This was still level with the top of the tank before it made a sharp turn and headed up to the fill cap. The cracks were where it was bent to go through a bulkhead. $10 a ft later of USCG fill hose and I'm a happy camper.