Water tank brush.It consists of a familiar-looking bunch of bristles at the one end, but the handle isn't solid plastic. Rather it's a container or reservoir designed to hold water. The two bits screw together, and the clip-on cap stops the water leaking out when you're not using the brush.As you use the waterbrush, water gradually seeps down from the reservoir onto the bristles. This means the brush bristles are permanently moist or damp.Ιn 2 sizes.