A closure for a container having a top opening bounded by a rim, includes a generally bowl-shaped body with interior and exterior surfaces and a hole formed on one side of the body. Extending about the body is a connecting section including a skirt and this connecting section seals the body to the container. The interior surface defines an interior space into which the container opens during use of the closure. The body is selectively deformable, upon manual manipulation, between an open configuration wherein fluid can pass through the hole and a closed configuration wherein one of the interior surface and the exterior surface of the body is sealed against the hole. In another embodiment, the closure is formed with a protuberance that projects upwardly from the top surface of the closure. A folding lip is arranged on the front of this protuberance and has a sealable hole formed therein.