The European Pulsar Timing Array (EPTA) network is a collaboration between the five largest radio telescopes in Europe aiming to study the astrophysics of millisecond pulsars and to detect cosmological gravitational waves in the nano-Hertz regime. The advantages and techniques of handling the multi-telescope datasets of a number of sources will be presented. In addition, the results of the EPTA timing analysis of the pulsar-white dwarf binary PSR J1012+5307 will be reported. Specifically, the measurements for the first time for this system, of the parallax, the variation of the projected semi-major axis and of the orbital period. Finally, the derived stringent, theory independent limits on alternative theories of gravity, with the use of this ideal laboratory for strong- field gravity tests, will be presented.