Apparatus is provided which reliably and conveniently controls fluid flow through a sidewall of a tubular string. In a described embodiment, an auto-fill sub includes a check valve disposed in a housing. The check valve includes a generally tubular flexible member for sealingly engaging a sidewall of the housing to prevent fluid flow through an opening formed through the sidewall. A flow deflector may be provided to prevent abrasive wear, flow cutting and extrusion of the flexible member. Other features may include a lockout sleeve and a piston for displacing the lockout sleeve relative to the housing.