I find that the cans that epoxy and hardener come in are not great for measuring small amounts, so I am planning on putting my hardener in an old plastic laundry detergent container that has a handy spout. The cap is also appropriate for measuring out larger quantities. All kinds of liquid products come in these kinds of containers.

I just checked out that the spouting system does not trap some of the liquid behind itself.

Obviously I emptied the contents and flushed it out well and dried it before I used it.

Beware some hardeners can eat some plastics. I would check a small amount first.