Ah. No wonder it didn't taste like tea. Did you have the liquid tested? Do you have a copy of the test results?
Was the tea sold in a bottle?
Is it possible that someone you know got into your cooler, drank the tea, and then peed in the container?
I think because of the two-week delay in time between the purchase of the tea at the gas station and the consumption of the urine by your wife, you would be hard pressed to prove the gas station holds responsibility. And a few gulps of urine is not likely to cause illness.
Without clear indication that the urine originated at the gas station or with the tea manufacturer, and with no damages, I do not see that you have much for a lawsuit.