With these pipes, never directly heat resin with a lighter/torch. The resin only comes as far as the top of the flowers.
You can add alcohol, salt or any cleaning solution inside the piece, shake and rinse off with warm water.
The outside can be wiped down with alcohol then rinsed off in water or just cleaned with water and soap.
Never soak the entire piece in alcohol. When resin sits in alcohol for extended periods of time, it will start to degenerate.