There's no real rhyme or reason to it. You won't know when it happens or how it's happening but Jojoba Oil DOES seem to relax your hole. I saw this recommended by the boys at gayfisters and asspig so i went to my nearest health food store and bought a bottle of the stuff to try a little experiment.
I have a 1 liter bottle of Pepsi here (3 3/8 inches wide, solid and non pliable as opposed to the 4+ inches wide anal toys that I can normally take) that I have been trying to swallow with my ass and for the past YEAR it would not go in due to my hips being too narrow. OR SO I THOUGHT...
A few days ago I bought the Jojoba oil and put a small amount on my hole and then a bit more and then a bit more. I wanted a nice thick layer so that it would penetrate and seep into my skin. I played with several of my warmup toys and then moved onto the challengers, 2 one liter bottles. The narrower 1 liter bottle went in without too much fuss so I turned my attention to the Pepsi bottle which is the widest of the 2. Up until that day, my hips would not open up enough to let that solid monster width through and then with a bit of patience I managed to impale myself onto that wonderfully filling bottle and it STRETCHED ME!!!! There was very little blood and no real tailbone pain so that was a pretty good indicator that all went well.
Now comes last night. I did the same to prep and warm up but this time I added a generous amount of Jojoba oil to my Crisco and applied a generous amount 30 mins before playtime. Well wouldn't you know it, my ass swallowed that wonderful Pepsi bottle almost to the halfway mark in no time at all! I don't exactly know why I am now capable of this otherwise incapable feat so I can only attribute it to the Jojoba Oil.
I could be wrong but it seems far too coincidental to dismiss it as the day I finally succeeded.