It is best to do this right before you bottle. If you run out of priming sugar before finishing the batch, you may substitute household cane sugar for the remaining few bottles. A small funnel is useful in this endeavor, perhaps a makeshift paper funnel. The carbonation of your beers will be dictated by the amount of priming sugar you use in each bottle coupled with the fill level of the bottles. Bottle Fill Level - One of the most important factors in determining the carbonation level of your beer is the level to which you fill the bottles themselves.
Overfilled bottle are likely to be under-carbonated.
Under filled bottle may be over-carbonated. The bottle filler in our systems is designed to achieve a perfect fill level. This may take some practice, but the skill comes quickly. You may wish to place the bottles to be filled in a sauce pan to catch any overflow you will probably generate. A room temperature environment is required to develop carbonation in a reasonable amount of time.