Here is a simple way to find the answer. Have your wife go in a graduated container for twenty four hours. You go in it once or twice to simulate an occasional friend. Divide the trailer's tank capacity by the measured 24 hour output. Now you have the number of days. If your wife balks at this, tell her it is the only sure way to solve the problem.
Please post to tell us what happens when you explain this to your wife.
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