Buckets to brewing vessels...

Hey guys... I'm new to brewing and right now I am working with 3 1 gallon demi jars.

I have about 8 square 4 gallon buckets that use to have freeze dried packaged food in them and I was wondering if i could use them to brew in.

The recycling number on them is 2. also the lids are not air tight... I was wondering if there is any way I could make them air tight?
I know i can buy a bung that could fit a hole in the top that I would cut myself, I just need them to seal.

any suggestions or comments are very welcome!
thanks,
Ben

8 years later... I got a bucket from the bakery used to store icing and the lid is definitely not airtight. I use 4 clamps to hold the lid down tight.