I too was sceptic at first. But practice is the only way to find out ...
I try to keep things simple :I just heat the straw (stolen at McDonnald's : they are large) with the flame of a BIC lighter and clamp/seal that end with my Leatherman pliers.
Looks like a good seal.
I am just waiting for better days, to leave such a piece of straw laying in the sun, to see if there is any vaseline leaking ...