You don't want to dump 3 bags into a larger container. The problem is not the plastic leaching but the oils in the food coating the inside of the can. These oils become rancid and contaminate the fresh food added to can.
Keep your food in the bags, open and use them one at a time. If you find a need to put food in can, keep food in original bag and put bag in can.
If you must dump bags of food into a can, line it with a fresh plastic bag every time.
I think Breck is saying that oils from the old food get on the side of the container and become rancid over time and can contaminate otherwise new / fresh food that you put in the container. I guess a person could wash the plastic container each time if you don't want to use plastic bags. I think I might use a tote and keep the bags intact as stated earlier or take a look at what Mitty suggested.Good idea, but if the plastic can can leach into the dog food, couldn't the plastic bag also?
