Three challenges down, and by now the team are starting to look a little worse for wear - and to be honest, they’re not smelling great either. So this time their challenge is to get themselves - and their clothes - clean. Jonathan has to build a washing machine from scratch. It’s a task that stretches his ingenuity to the limit. His solution is a toploader made from a bucket, a bicycle wheel, some tennis balls and an old power drill. That turns out to be the easy bit - it's the electronic valves and the control system that really tax his brain cells. Will he have to head off for a launderette after all? Ellen helps him out by going in search of a plant that will provide the washing soap. She finds what she's looking for, yucca, but will the strange looking liquid she gets out of the plant really make clothes cleaner? The rest of the team attempt different ways to reduce body odour. Hermione makes a deodorant out of rocks. Things don't entirely go to plan when she has a nasty surprise with a supposedly heat-proof beaker. Mike sets his sights on stopping sweat by creating the same chemical that's used in most commercial antiperspirants. Using aluminium foil and household bleach he sets to work. But all he seems to succeed in doing is creating some very nasty smells. Lastly, Ellen makes a triple action botanical roll-on using a variety of local plants. The three deodorants are put to the test in an armpit sniff trial with Kate as the sniffer dog. For Kate this could be a particularly rough episode of Rough Science.

• Kate Humble
• Iain Stewart