I go on the extreme side of things. I get a nice amount (couple gallons) of water and add baking soda to near saturation. Meaning, I add and stir in baking soda till it takes 15 seconds of stirring for the powder to dissolve completely in the water and become clear. You could possibly get away with less, but for less than $1 per box of baking soda, I play it more safe than sorry.