What did you say?

This is a translated transcript from an actual dialogue I had with our guard the other night. It is a perfect example of communication between two people neither of whom speak the common language fluently. Background notes: Omo is laudry detergent that is commonly used to wash the car; guards do more than guard, they also wash cars, sweep, and water plants.

Guard: Sir, we are out of Omo.
Me: That's okay, you don't need to wash the car.
Guard: Can I have money to buy some Omo?
Me: No. You don't need to wash the car.
Guard: I use Omo to wash the car.
Me: I know, but you don't need to wash the car.
Guard: You can buy Omo at the boutique for 20 cents.
Me: I know. But you don't need to wash the car.
Guard: Okay.

The next morning as I left for work, I found that he had washed the car, apparently with only water (no soap). Looking back, I think he understood me to say "you don't need it (Omo) to wash the car", which would be a very strange thing to say, thus he kept questioning it.