(The aliens used my account again)
Buy 5 sausages of visibly different diameters, smallest one
what you think your ass just can fit. (Don't start too big.)
Now, first plug is the one sausage that perfectly fits your ass,
try to push in larger and larger until you find that one.
Don't let it slide all the way in; use something to keep it in while
it is sticking out two inches, maybe a string or a stick.
When it has done its work (for at least an hour), take the next
larger size that didn't fit your ass before. Keep this one in at
least an hour as well, until you can take the fattest one.
Probe with the fattest girth one for 1 hour! Done!
For extra luck, use spicy sausages!