So, you will want two large buckets (each with the capacity of a couple of gallons). You want one to be hot, and one to be cold.
The one can be water that is as cool as it comes out of your tap, and use just about as much ice as you have water and put it directly into the bucket.
What you will end up with is a liquid solution that is just above the threshold of freezing.
In the other bucket, you want water that is somewhere between warm and hot. If you want to be really precise, it needs to be 105 – 110ºF.
It will feel hot, make no doubt about it, but it should not feel dangerously hot – you will not burn or harm yourself in any way. Briskly hot, but not too hot. You can also feel free to test with either a thermometer or where your skin is most thin (along your neck or your wrists).
Next up, you will want two hand towels. Washcloths are a little bit too small for what we need, so what you will want are two hand towels that are somewhere in between a washcloth and a big bath towel (if you can wrap it around your whole body, it might be a little bit too big).
Drop both towels into their respective buckets – one hot, and one cold. For the purpose of keeping this as part of a cycle, you will also want to have a timer handy.