Factual programme. Ed and Oucho are travelling all over the country making inventions from bits of old rubbish they find in the back of their van.
Here, they are trying to build the Dirt Rumbler, a tank that waterbombs people. It starts off well, until Oucho realises their catapult is a dismal failure and only manages to fire water bombs at their feet. With the Big Big Cheese on their backs, will their general uselessness and lack of science know-how stop them from building the Dirt Rumbler in time?