We could use 20 foot above source, and 20 feet fall from source to outflow, no pump at all. How we start the siphon is not part of the construct :-).
peak level of pipe 20' above source
source 0 feet
outflow 20 feet below source
Pressure with siphon flowing will be 4.3 PSI
Pressure when the "up" leg is working will be 4.3 psi, if we let the siphon empty out once only the "down" leg is full it will be 8.6 psi.
If we think about how we have seen siphons work, and how they behave when they collapse this is exactly how it happens. When the source end runs dry the outflow increases because it is no longer lifting water from the source end to the peak elevation of the siphon.....flow increases as siphon collapses because the pressure temporarily increases.