I made some crude attempts when I was a kid and couldn't get any real diapers. I would fold up some old t-shirts and put them in my underwear. I don't believe I ever actually used them, they were more for the feeling.
When I was younger, I used to make makeshift diapers often. They were very feeble attempts, often involving boxers (I didn't wear briefs :frown or towels. They didn't hold pee in, but at least they contained #2. I don't really think there's a good way to make a makeshift diaper. You can just throw something together and hope it works.
I made one attempt when I was younger and less intelligent. It involved me putting on about 5 pairs of briefs and then proceeding to wet myself a couple times. I was at my grandparents house at the time and thus had no access to a washer and dryer. Also, I had no underwear for the rest of the week (I don't remember how I managed to survive that). Needless to say, it did not go well and scared me out of making another such attempt. I guess if I had kept trying I would have developed some better methods, but you still can't beat the real thing.
Ahh...the good ole days of towels, plastic bags, kitchen roll and packaging tape. If you're creative enough, you can create your own diaper with those four items, but it will obviously never be like a proper disposable adult diapers.
Unless you flood it, the towel should easily contain your pee, and the plastic bag should ensure it doesn't leak right to the floor. However, I would suggest you do not sit or lay down with your makeshift diaper and take it off immediately after using it and take it off right after you've wet it.
Making a "diaper" for messing is even easier - all you need is a plastic bag and tight underwear. No instructions required really - place plastic bag in your underwear, pull it up, go. Add a layer of kitchen/toilet paper and you can even dispose of the evidence easily by flushing it down the toilet.
Easy, take some old briefs put them on and then take a black garbage bag and make leg holes, then slide it on over the briefs. Put any excess garbage bag at the top into the underwear and then you will have something that's like a diaper. Then take packaging tape and take it around the leg holes and around your waist. It usually prevents leaks if you do it right, you can even sleep in it
What I've done that's successful is towels, safety pins, a trash bag which you poke holes in the bottom two corners and use as plastic pants, the thing is you want to run it through the wash afterwards, and if you do #2 in it you want to scrub it in a large sink after you remove the excess.
For girls: Put on at least 5 or 8 at the most, cotton panties. Regular cotton ones only, NO thong, boy shorts, or bikini, it will not work good. Also MUST be cotton. The do the trashbag with the leg holes like others were saying. For extra absorbancy put a super maxi pad or overnight maxi pad inside the first panty that you put on.
For Boys: Put on at least 5 or 8 at th most briefs (whitie tighties), and put a trashbag with legs holes over top of it. Also can add a panty pad for extra absorbancy.
Take 20 sheets of tolite paper and fold it so that it 4 sheets across
Put in back of Brief underware
Now Take 4 puffs tissues and line 2 on the bottom and 2 in back
Ware and Mess (piss through the front of the briefs through the hole)
For added cushining, fold tissues and put them under tissue lining.
Lining is totaly flush-able even for septic tanks + if done right, will not stain briefs
I used to get one or two of the fancier (softer) bath towels from the store, fold them into thirds, then sew them together by hand. I think I used to use a line of stitches about every two inches. Sew them length wise and you're pretty good.
If you get some flannel or birdeye from the local fabric store you can get a cool print for the outside layers, the terry towels will act as your absorbant layer, then it feels great and holds a lot.
i used to make make shift nappies out of sanitary towels, plastic bags and old torn up sheets plus tape.
until i discovered how to make nappies that absorb as much as the real thing.
i've made some pretty absorbent nappies.
cut 2-4x lengths of cotton wool or lint padding strips.
then put a bigger piece of the liner underneath, add approx 400g of absorbent gel crystal powder to it, then add another length of cotton wool or lint padding strips over it and glue the edges so the absorbent gel crystal powder don't fall out.
and so that the absorbent gel crystal powder is sandwiched in between.
u can repeat the absorbent pads as many times as u want to make them absorb more.
glue a piece of one way gauze to the last sheet of padding.
then wrap the liner round the whole pad and glue it's edges together.
then place the giant finished pad in one of these plastic wrap around diapers:
plastic tie up diaper outer:
everything can be bought online easily.
plastic tie up diaper outer can be got from save express.
absorbent gel crystal powder and other things can still be got easily online.