A combined relief valve and lid structure is provided for pre-mix beverage and syrup containers having a tubular body enclosing a relief port in the lid, an annular valve seat surface about the relief port and raised higher than the lid surface and drain ports extending from the valve seat surface down to the lid surface to enhance drainage of the entire internal portion of the valve body. The relief port is closed by a spring biased poppet and has a biasing spring held in place in the top of the tubular body by a one-way detent and retainer clip arrangement which must be destroyed to remove it from the valve body to gain access to the relief valve poppet. The valve cannot be tampered with unless this retainer clip for the valve spring is destroyed. The retainer clip is ported to permit cleaning steam or other fluid to enter the top of the valve and drain off through the drain ports without accumulation of condensate or residual fluid in the valve. The poppet is basically cylindrical with relieved vertical side portions or flats to enhance drainage and exposure of the valve surface for cleaning.