I wait until the tribe who always tell the truth take the turn to guard it and ask them which tent the statue is in.
Edit! I came up with a better answer after reading the riddle again.. Read below V
To know which tribe he is from ask him if he has a 500 meter penis. If he is from the tribe which lies he will say yes but if he is from the truth-tribe he will say no. if he is from the truth-tribe ask him which tent the statue is in!