Pirate is right - find the leaks before you start doing anything else.

When the hulls are leaking that much, you will only need a bit of air pressure inside and you will hear the air rushing out through the leak(s).
For finding the smaller leaks, an alternative to a tea-towel is one of those little hand spray bottles with washing-up liquid and water in it.

I don't use a bike pump. I fitted a pop-top off a drink bottle onto a spare hatch cover. It only takes 3 -4 breaths to get enough pressure in the hull. Then you push the pop-top closed and go hunting for leaks.

Like I say, with such a big leak you wont have to look for long.