I regularly take caster oil with the aim of being caught short and pooping my nappy (I'm English so diaper for you that speak USA English).
My usual dose is 150ml (4-5floz) which I take strait from the fridge in a glass. Just swig it down in one gulp then mouth wash and gargle in a small glass of dry white wine. That takes the taste away. Don't get drunk - one small glass only.
It's a good idea to be in a nappy before you take the laxative. But asap afterwards - there are horror stories of CO kicking in in less than an hour.
Usually I take an anti-diarrhoea such as Imodium for three days before hand to ensure a full bowel.
For me the effects of the caster oil start in about 3 hours with a rumbling tummy, vague discomforts in my belly and the occasional internal stitch. After about 3 1/2 hours my bowels start to spasm in waves. To begin with gentle urges to void that quickly become closer together and so much stronger. By the 4 hour mark my nappy is usually messy and wet although I have tried desperately to keep it clean.
From then on in for two to three hours I need a bowel movement frequently. (As my nappy is already messy I like to stay relaxed and just let the urges to pee and poo happen.) If I think my nappy is getting too wet - with the chance of leaking I change quickly with only a wipe down into a dry one.
Usually my tummy has returned completely to normal four hours after I first messed my nappy, so I get cleaned up properly, but I put on a clean dry nappy - just in case!
I enjoy my caster oil days - they would be so much better if I could share them with 'special' friends!!