if you dumped the beer and they do not have the cup you had the beer in, they cannot prove you had an open container, which doesnt matter anyways because(and this could be different from state to state) you were not in a vehicle with an open container. if you were outside of your house on your neighbors porch, how can you be hit with "open container" when you and your neighbor are on his property and drinking a beer, if it was against the law, they would be summonsing people left and right. did they make you take a breathalizer test???? if not, they cannot prove you were drinking. but regarless of all that, if the first individual did not identify themself as a police officer and you started to walk away, then you are fine, now the second person did identify themself and you stayed there which is good. just like it was said before, go in and state your case exactly how you did here and you should be fine. hope all goes well for you.
