I am making an irrigation layout at the moment :13mm and 4mm piping - for some
raised beds

I need to cut the 13mm to quite precise lengths with L's and T's. I was then
finding it quite difficult to push the piping over the barbs with the pipes in
situ

Ding!!

Put the end of the pipe in a jug of near boiling water - and then the piping
just pushes on with no problem after becoming quite soft.