Step 1: The first cut is the deepest.....
*a t-shirt (sleevless/vests type works best)
*bootlace or other strong cord thats long enough to go round your waist
*drawstring toggle (i never throw stuff out so had one off an old rucksack, but you can buy them in craft stores)
find the hem and snip open the side seam (about 1cm) to open this channel