The sweet potato is a root. It sprouts from the end wher it attaches to the vine so it is important when starting in a vertical position to have the proper end down.
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You may burry the tuber horizantally in the pot for sprouting.It will be easier to remove the slips.Sprouts are the end connecting vine.

Pic. of the sprouts.
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g'day weedlady,

just simply cut the tuber in 1/2 crossways and stand each cut end in a little water enough to keep the ends moist, don't let the water evaporate away top it up, and those ends will bud, at which stage when the shoots reach about 4"s cut that section out and divide if you wish and plant them out no roots are need, though the tubers may grow roots in the water.

so as you remove those growth sections and return the tuber to the water it will again grow shoots.

len

Here is a link that might be useful: lens garden page

Do sweet potatoes take up a lot of space to grow?
I think I want to grow them ... the leaves are also edible (cooked) ...it would be nice to have them on hand.