Pony and trap

Rubbish, nonsense, garbage. Shortened to 'pony' in the wild — 'that film was a load of pony' means it was dreadful. Same rhyme also covers the literal toilet meaning, but in everyday use it's the 'rubbish' sense doing the heavy lifting.

The literal one: a number two. Less commonly used than the 'rubbish' sense, but it's the original rhyme. 'Going for a pony' lands if your audience is in the know.