that's a good possiblity depending on the setup. More than likely you just have "T" connected in-line to your seawater pump. Easiest way to find out is to turn the water on your connection while out of water and see if it drains out the bottom of your outdrive (where the intake for water is). You may be fine even if it does, but I would say it would also suck air in as well, which you don't want.
Typically flushing would be a few minutes.
