The stirrup vase is thought to have been a container for oil and in ancient Greece one of the uses of oil was for washing oneself, much like toilet soap. It has a solid central column with a handle on each side of it and in front a spout. This peculiar arrangement should have a purpose and I suggest a possible one.

Hold the hand palm upwards and insert the second and third fingers through the handles, gripping the spout between the tips of the fingers and the column between the lower joints. Then, keeping the palm upwards, bend the fingers to tilt the spout over the palm of the hand. Oil will then run or drip out into the palm and the other hand can be used to smear it on the user's body without putting the stirrup vase down, so solving the problem one has nowadays of losing the soap in the bath.