11.4.8. The interior and exterior walls of the tank and the welded seams and other joints must be(1) smooth, washable, impervious, corrosion-resistant and free of cavities and cracks;
(2) designed to protect the milk against any source of contamination;
(3) non-toxic and resistant to washing and sanitizing operations; and
(4) unaffected by milk and the other food products referred to in section 11.4.6 and constructed or made so as not to affect them.
The interior wall of the tank must be of stainless steel.