Razorri RZ-08 Sous Vide Precision Cooker Machine Immersion Circulator, with Digital Timer, 800 Watts, Black (cooking balls)

keeps the food down and heat in

I've been cooking sous vide for more than 6 months and I have been using ping pong balls to prevent water loss during long term cooking. The smaller cooking balls have proved to be far better with very little water loss from evaportaion. Highly recommended.