Ask the swimmers to stand with one arm behind their back and one in the water ahead of them, thumb pointing to the ceiling.
Throw each of them an imaginary ping pong ball. ask them to place in in front of the palm of their outstretched hand. Now move the ball across, quickly flip your hand over so the ball stays in the same place and push back.
Keep the sweeping action going until they get a good rhythm, slow sweep with fast turns, then ask them to lower their body down so that the arm is completely submerged.
“Can you feel how thick the water is? That is the feeling you should have on every stroke”
Now use both arms at the same time, turning just before they meet.
Apply that to whatever stroke or drill you are practising. For example, breaststroke – press the balls away from you, then bend your elbows and squash the ping pong balls together; Front crawl- push the ball towards your toes then reach forward for another; sculling – small fast sweeps.