In addition to having to sell items one by one it also appears to be impossible to poison the booze tub. When it opens up the combine pop up it shows that there is nothing in the inventory. My character is carrying multiple bottles of poison but I see 0 items when it comes to what's available to combine.
https://stadia.google.com/capture/b676c2de-8fa3-4ba1-8d26-35bb5eb6fa8c