Chris - Didn't hear this ref on J Vine show, but this is not only true, it has been kicking around since Victorian times.
The principle is very much like making tea with a tea-bag.
Take a small hessian sack, half fill it with sheep droppings (preferably gathered fresh from the field, although you can also use dry cow-pats) tie the top & hang over the side of a *water tank and let it soak for a few days.... the mixture is ready for use when it resembles tea. Before use, be sure to stir well to mix sediment from the bottom
*Personally I think the capacity of most water butts would be too much, hence you would need a huge sack of poo, otherwise the mixture would be too weak. I think a small hessian sack & something like an ex-household cold water tank would be best.
The resultant liquid manure is great stuff!