Are you competing in the Iron Butt? Riding across the continent? If so, then the Japanese toilet company Toto has the perfect trike for you. The toilet itself is just decorative, but the engine runs on real manure:
The Neo, a product of three years of research, development and design, is based on a 250cc trike, with a built-in toilet for a seat. The rider does not contribute to the fuel supply of purified and compressed livestock waste. So for now, this model’s bio-gas comes from the Shika-oi, in Hokkaido. As an engineer explained, “The waste and household water are converted to methane gas by fermenting, and the methane gas is converted to bio-gas by purifying.” Only the bio-gas ends up in the bike, so there’s no manure on-board.