I'm in the process of installing an Ideal Isar 30HE boiler, and the manual
says if I'm connecting the condensate pipework to a soil stack (which I
will
be doing) that I need to fit a 75mm trap.

Can you just use a washing machine style trap and stick the hose in the end
with an air break? Only do this if the boiler manufacturer is happy to do
so, as with some designs, they might worry about it exhausting through there
if the boiler internal trap is empty or not specified.

Christian.