can I put anything in the top container to help displace the water around the sides? The bins are the same size and weight but I don't have enough weight inside the top one to push down the water. I was thinking of bricks or a large bucket of water but I didn't know if that would be unsanitary. Thanks for any help.
If you wash and dry the bricks/stones beforehand, why not.
Alternatively you can bind the top bin down to the bottom one, if feasable.