Last summer I helped my friend make a Santorum Slip n Slide, named after former Senator Rick Santorum.
Here's how it's done:
We found a 1 gal jug of IDGlide. ID Lube has a list of places that sell their products. You will need 1 gallon of lube as it is to be the backbone of the 'slide, it makes all the difference, just like with sex.
The plastic sheeting we got from Lowes. If you can, buy the thickest they have. It may be a few bucks more but will last much longer. We bought the thin stuff and the plastic ripped and tore easily.
Our ingredients also included 2 bottles of dish soap, 2 bottles of Hershey's syrup, warm water in a bucket from the shower and the lube. Towards the end there was milk thrown in as well.
Anyone that goes to a slip n slide wearing anything other than old shitty clothing isn't doing it right.
It really is that much fun