Riddle

Nobody empties me, but I never stay full for long. What am I?

Choose an answer

A.The sun
B.A glass
C.A balloon
D.The moon
Hint: It's a 2-word phrase with 7 letters, starting with "T".

Answer

The moon

Why this is the answer

The moon cycles through phases, changing how full it looks.

This riddle is filed under Hard/Difficult Riddles and rated Medium.