replace gas cap, tether?

Depends on where you get the cap. Most after market ones don't have a tether so you could just cut it off.

If you buy a new one from a dealer you get a tether.

Why do you need a new cap?

thanks, Steve. I've twice got the trouble code for small EVAP leak, the one that's usually due to the gas cap.

Also, look at this:

I'll just get one from AdvanceAuto - though not sure whether to get a locking one or not.

I would test the cap first. Small leaks can also be from rusted purge lines, vent lines and the solenoid that closes off the vent for testing. If you think it's the cap you can test it by using a time old test. Grab a plastic sandwich bag, place it over the fuel filler and put the cap back on. Clear the code and make sure the conditions for that test are there and see if the code comes back. If it does it isn't the cap. Since the conditions for that test are specific you can remove the bag if they are not met.

The drive cycle begins with a cold engine startup. The IAT must be between 32 and 85 degrees F. Engine Coolant Temperature (ECT), must be less than 127 degrees F.

Start the engine and allow it to idle in Park for one minute. Within the first minute and a half, accelerate at 1?4 to 3?4 throttle to

50-55 mph. Hold that speed for 2-3 minutes. Decelerate to 0 mph without braking, then idle for 1-2 minutes. Accelerate to 55 mph, using 1?4 to 3?4 throttle, then hold a steady cruise for 10 to 20 minutes. Return to 0 mph with the engine idling in Park, then turn the ignition off.