No, it is not possible to siphon water from Bucket A to Bucket B and from Bucket B to Bucket A simultaneously using a single siphon.
A siphon relies on the force of gravity to move liquid from a higher level to a lower level. When a siphon is set up, the liquid flows from the higher container (Bucket A) to the lower container (Bucket B) due to the pressure difference created by the difference in height between the two containers. This pressure difference creates a downward flow.
If you were to connect the two containers with a single siphon, attempting to siphon water simultaneously in both directions, the pressure difference required for the siphon to function properly would not be established. In order for the siphon to work, there needs to be a clear distinction between the higher and lower levels of the liquid.
If you attempt to siphon water in both directions, the pressure would equalize, and the siphon action would be disrupted. The water would not flow in either direction, or it might flow in a less controlled manner.
To achieve simultaneous siphoning between two containers, you would need to set up separate siphons for each direction, ensuring that there is an effective height difference in each case.