You can isolate the fuel lines by using a pair of forceps and your inline shutoff valve.

Clean the outside of the UAT and make sure it is dry.

With the lines isolated and your UAT full, squeeze the UAT and look for leaks around all of the fittings and cap.

After squeezing the UAT and then releasing it (assuming that it collapsed) if there is a leak you will see tiny bubbles where the leak is along with a wet spot of fuel.