Container for collecting waste lubricant

A container for collecting a liquid lubricant, the container comprising:

• a housing having one end formed with an inlet opening connectable to a source of the liquid lubricant, an inner surface, and an opposite end;
• a cap closing the opposite end and formed with a vent hole open to the exterior;
• a piston shiftable along an axis inside the housing, sealingly engaging the inner surface of the housing, subdividing the housing into a front lubricant compartment into which the inlet opening opens and a rear compartment into which the vent hole opens, the piston being slidable on the inner surface of the housing between a front position close to the intake opening and a rear position close to the vent hole such that as the liquid lubricant fills the front lubricant compartment the piston moves into the rear position and expels air from the rear compartment through the vent hole;
• a cap seal formation on the cap;
• and
• a piston seal formation on the piston axially engageable with the cap seal formation for sealing between the piston and the housing around the vent hole only when the piston is in the rear position, one of the formations being an annular seal surface and the other of the formations being an elastomeric seal ring engageable with the annular seal surface only in the rear position of the piston.