JZOrewa said..
My main bladder was leaking on one of the ends, so I just tied a knot and it doesn't leak anymore. The main bladder (I have a F-one Bandit) is at least 20cm longer on each side than the leading edge of the kite, so that's enough for the knot. Off course it just works when it is on the end of the bladder.
Better with an iron & baking paper folding end over a couple of times, lucky if he leak was in the end of bladder and there is plenty of spare. Sometimes needs a few goes, but the heat of the iron seals the latex together and leaves a nice flat section to match the tab at the end.
Fixing a large hole in the middle of the bladder is a whole different ball game, you could try an iron with some spare bladder material, maybe there would be shrinkage so glue better? Never tried so cannot say.