there is a much lower risk of boom squish with smaller amounts of water under more weight from a bench but think that you would be best palcing them near the outer edge to avoid the risk of them getting hot
enough to convert to steam and work either a hole, pressure point, or weak spot that encourages random cracking or something, im all for getting water in there and using up those beer bottles but they may just cause some kind of problem at some point
i saw this thing
online where a guy stuffed a beer bottle with organic matter and innoculated it with
mushroom mycelium, fruiting an oyster mushroom from the mouth of the bottle, i thought it was quite cool and hope to eventually replicate it after collecting more
coffee grounds from the coffee drinkers in the family