The thing is, what is the nature of the thing he drank? If it was Fey in origin we can get all sorts of silly, if it alchemical we can get pretty weird too, but if it was just bad that is less interesting.
I would play up the toughness of the dwarven constitution. The 'poison' would have killed anybody else, but for the dwarf it has just given him really bad gas. Not normal gas mind you, actual toxic sulferous gas that comes out both ends. He can belch/fart sulfur like a dragon and it stinks to high heaven. He needs to keep drinking huge quantities of water or else it starts burning and he literally breaths out burning gas.
It can be silly and a laugh at the dwarfs expense, but also rather intimidating. I would not stand up to an angry dwarf that blew sulfur out his nostrils.
<edit> Maybe it was a potion of fire breath that was part way through being made. Or a cold resistance balm that was not meant to be taken internally.