Marm, I've done it to a number of briars with great results. Doesn't take much to tighten the stem right up. The only thing to keep in mind with this pipe is how much softer the plastic connecters are.
I would just lightly pass a bic lighter flame over it maybe 5-6 times, barely letting the flame lick the plastic for a second at a time and turning the plastic so it heated evenly. Then try to widen it, if it wasn't quite soft enough, pass the flame over 4-5 more times, until it will stretch some with whatever tool you're using.
Make sure it cools completely (you can dunk it in water to instantly cool it) before you insert it into the other piece.
If it is still hot when you insert it, the other piece can deform it, making it loose all over again.
Of course, if you flare it out TOO MUCH so that it wont go in, you can heat it again, and very gently push it straight in without wiggling it so that it shrinks again.
Try to get it right the first time though, heating it over and over again can eventually mess up the plastic.