Where do I throw this away?
BOO-toh — the double 't' makes a short, crisp stop; do not linger on it.
Use this when you are not sure which bin a piece of rubbish belongs to. It works at home, in a shared building, or when a friend or neighbour is nearby. It is casual and perfectly polite.
Buttare means 'to throw' and is the standard everyday word for putting rubbish in a bin. The question is simple and direct. Italians will immediately understand you want recycling guidance, not just a bin location.
Dove lo metto?
Where do I put it?
Even shorter; 'lo' refers to a masculine object already mentioned.
In quale bidone va?
Which bin does it go in?
More specific — mentions the bin (bidone) directly.
Dove si butta?
Where does one throw it?
Impersonal form; slightly more neutral and very common.
In Italy the lid and the container of the same product often go in different bins, because materials are sorted by type. Many newcomers are surprised by this level of separation.