46.2. Standard sand-filter beds built under a non-watertight secondary treatment system: A gravity feed standard sand-filter bed built under a non-watertight secondary treatment system must comply with subparagraphs f, h and h.1 of the first paragraph of section 21, section 25.2, subparagraph a of the first paragraph of section 27, paragraphs a, b and c of section 31.1 with the reference to section 28 in the latter section replaced by a reference to section 44, subparagraph b of the first paragraph of section 37, with the necessary modifications, and subparagraphs a, f, g, h, j and k of the first paragraph of section 41.