The article describes a newly developed calculation technique and choice of the geometrical parameters of the solar collector with the siphon effect. The dependence of the cross section of the pipe on the flow time for different values of the head is also shown. With an increase in the siphon head, the flow time of the liquid increases. This is explained by the fact that with increasing head the hydraulic resistance of the siphon increases, which leads to a decrease in the velocity of the fluid. For the first time, a relationship determining the time of fluid outflow in dependence on the geometric parameters of the solar collector is settled. The developed technique allowed to establish that the local hydraulic resistance and friction play a significant role in the heat carrier flow rate.