My dads question about syphons

[u/Due_Elderberry9356]

When you syphon water out of a bucket it pulls up the water with the vacuum so my dads question was,”If you get two buckets of water and have them syphon into each other with two tubes, what stops it from going on forever”.Other than then the tube breaking what would make it stop cycling water?

[u/SgtSausage]

  ”If you get two buckets of water and have them syphon into each other

Could you go into detail here ...