Hall, Public Chamber
A Viking will empty his mouth of all its dirt in the great hall. They all get together in some kind of public chamber and dish all the dirt (literal and figurative) that they've got.
Picture a long Viking hall, with a big table and tons of chairs. All of the Vikings are gossiping and sharing all their dirt on their enemies.
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While the Vikings gather to spill the dirt in their hall, they also stuff their faces with doughnuts (どう). Ah yes, Vikings love to eat doughnuts when they talk trash.
Now picture all of the Vikings in the hall spitting dirt with one breath and shoveling doughnuts in with the next. It's pretty gross!