I have tried to use the compression couplings sold in the local orange big box store to repair some existing irrigation lines in my wife's flower beds it's 5/8" tube. I cannot get the tube to go into the coupling any ideas what I'm doing wrong?

I fill a thermos with hot water when I'm doing a lot of irrigation work and dip the pipe into it. It makes a huge difference with how workable the PE tubing is.Another vote for hot water, a kettle works perfect is the wife is out.
Soap helps also
I'm talking about the 1/2" diameter tube that you attach drip tubes to.Funny pipe and drip lines are two different items.
Which type of pipe are we talking about?
