There are a number of styles and most come with a simple wire hanger to use with cages. Be sure that the tip of the water bottle is well above the bedding. If the tip comes in contact with the bedding or other material it will leak. A good premixed gerbil food is recommended. It is now easy to get the right combination of protein, minerals, vitamins, and bulk.
Sunflower seeds tend to be very high in protein, and, there for, fattening.
Each morning when I feed my gerbils I pick out the majority of sunflower seeds. I place them into a small container. Then several times a day I hand feed them to the gerbils. This has a double benefit. First, they do not get the excess protein.