Disclosed is a check valve for preventing liquid from entering an attached tube. The check valve includes a cylindrical housing having an inner surface and a removable plug that is at least partially within the housing. The plus has a side wall with at least part of the sidewall sloping in an inwardly direction from a top surface to a bottom surface towards a central axis. The side wall is operable to contact the inner surface of the housing and form a seal, thereby preventing liquid from passing through the housing, the housing being fixedly attached to an inner surface of a tube.