Using recent work of the first author [3], we prove a strong version of the Manin-Peyre's conjectures with a full asymptotic and a power-saving error term for the two varieties respectively in P 2 × P 2 with bihomogeneous coordinates [x 1 : x 2 : x 3 ], [y 1 : y 2 , y 3 ] and in P 1 × P 1 × P 1 with multihomogeneous coordinates [x 1 : y 1 ], [x 2 : y 2 ], [x 3 : y 3 ] defined by the same equation x 1 y 2 y 3 +x 2 y 1 y 3 + x 3 y 1 y 2 = 0. We thus improve on recent work of Blomer, Brüdern and Salberger [9] and provide a different proof based on a descent on the universal torsor of the conjectures in the case of a del Pezzo surface of degree 6 with singularity type A 1 and three lines (the other existing proof relying on harmonic analysis [18]). Together with [8] or with recent work of the second author [22], this settles the study of the Manin-Peyre's conjectures for this equation.1991 Mathematics Subject Classification. 11D45, 11N37, 11M41.