Ok, I have a similar garden-hose fitting I put on my X22:
http://www.epicmarine.com/forum4/index.php?topic=1300.msg11432#msg11432With the Engine off, and the gardenhose on, the water is going to take the path of least resistance: flow out the strainer, down and out the intake port on the hull bottom. This is the water you see coming out from the middle of the boat. When the boat is actually in the water, and engine on, the cooling water is sucked into this same port.
Now when I start my engine, running off steady garden-hose pressure, the sea-pump swallows Most all the water coming from the hose... there's still a little coming out the hull bottom. Eventually the engine, heater, and exhaust manifolds fill with water and purge itself out the Exhaust ports. If you don't see water coming out the back (Exhaust ports) in under 45 seconds, there is a problem. And at an idle the water pulsates out the exhaust... like breathing.
Do you have a shower (in the trunk)? Make sure the valves are closed.
Follow the hose back (towards the stern) from the sea water pump to the hull intake. Loosen each hose clamp connection, break the hose loose and reseat it... it's rare, but the connection may be water tight, but no air tight. if there's an air leak it's probable it's between the garden hose and sea-water pump.
Here's the parts along this water path: the sea-water pump is fed by a hose from a straight metal cylinder. This is the Tranny cooler. the water flows thru the center of it. Hydraulic fluid in the outer jacket is cooled; note the hydraulic hose connections. On the stern side of the tranny cooler, the hose will attach to pipe fittings, if you have a shower or gardenhose connection. Retignten the pipe fittings into one another too. then it there is the intake filter (a clear cup with a metal screen inside). then an elbow pointing the towards the bilge. And finally the water intake/pickup in the hull.
I had a very similar problem. There were no water drips at all at any connection. yet Engine was overheating. Pulled it all apart (as described above) and put it back together. My overheating problem went away. Never found a smoking gun.
Good luck