MythBusters Season 8 Episode 8 (MythBusters s08e08) with title “Waterslide Wipeout” airs on Wednesday, May 19th 2010 at 09:00 pm via Discovery.
Here is summary for MythBusters Season 8 Episode 8 :

On this wet and wild episode, Adam and Jamie tackle the biggest, dirtiest, most vertigo inducing build in MythBusters history while Kari, Meanwhile Tory and also Grant deliver the goods, to find out if taking only right turns can save you gas.

Few hours after original series aired on TV, online streaming video for MythBusters Season 8 Episode 8 usually available on Net and of course, if video available, as soon as possible will show you where you can watch this episode for free.