I believe German custom is to tovel keilim that are made out of plastic. But I think that only applies to hard plastic, since it is given to becoming a permanent keili, and not soft plastic which is flimsy and disposable.
In general, one does not need to tovel a disposable item. Even if one reuses the item, if it is intended to be disposable (and the person will eventually dispose of it) it does not require tevila. Hence, a soda can, or a snapple bottle may be refilled with water without tevilla, because they are disposable.
It follows that if one would decide to keep an item for permanent use (say a soft drink that comes in a nice glass container, such as I’ve seen POM tea come in), it would be proper to tovel it before reusing.
As with any such issue, the best thing is to find out what you can and then ask the Rov whose psak you follow.