I guess from your info thingy on the side if it's under 3m you don't have a hollow hull? In which case the "fil lit with water" trick is likely going to work best.
If that is just "default" and you do go the pressure route, you won't need much pressure to simulate a leak. Also to prevent creation of a floating skating rink, concentrate on fittings & fixings first. That way you don't cover the whole boat in slippy soap. I used a 50 / 50 washing up liquid when looking for a toob leak. It gives a reasonable mix of bubbles and ability to clean it off afterwards.