With that size leak you should be able to put water in the hull with a garden hose and see where it comes out.
I would never pressure a hull with water and ideally not fill from the inside to find holes.
Having said that I found one that I had been looking for for about 12 months by forgetting to empty 1/2 cup full out and then spotting a small drip; It was an odd hole as it closed up under pressure (I'd been looking VERY hard for it with the soap-and-blow <img src="http://www.catsailor.com/forums/images/graemlins/wink.gif" alt="" /> method......)
