The jug is just an over fill. Wait until the car is cold and pour some 50/50 coolant in the radiator to cap it off. Depending on how much you will need to pour and how often will indicate how bad the leak is.
Located at the front of your engine bay will be the radiator.
Make sure that the overflow bottle is at least two thirds full the next time you drive any where. As soon as you stop some where, open the hood and see if the water is boiling in the bottle. If it is, then you're looking to replace head gaskets. If it's not and just dripping out, it's no big deal. If you were smart, you would have your radiator flushed and fresh coolant/anti-freeze put in. Orange indicates rust and you'll lose your radiator in time.
The jug as, Soul fly pointed out, is just an over fill. If you have a leak somewhere in the system it will suck air, when it cools down, rather than liquid from the overfill tank. Pour liquid directly into the radiator, and get the leak fixed, ASAP!
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