Good to see you back on again Matt.....
25l jerry cans will involve a hell of a lot of fittings and messing about.... Is there no chance of getting something along the lines of 200l plastic drums... After messing about 100l half drums and organising the piping into, and then drainage pipework, I wouldn't want to be fiddling with anything smaller for growbeds if the system is of a reasonable size....
Anyway, the pipework I have used is the 19mm and 12mm trickle irrigation piping, very easy to work with, and cheap....