Hydro are a closed loop system. They will purge themselves without doing anything else. The hydro pump has a large cavavity which the charge pump will fill full of oil, they actual pump then draws oil from this cavavity. As mentioned above, it is best to pre-fill the new filter. Oil filter leak - make sure that the gasket is on the filter correctly and that the old gasket is not stuck to the filter head. Lubricate the new gasket with a little oil before installation. If you still have leaks check the filter head gasket area for any scratches or gouges, also make sure filter head gasket area is clean. If you still have leaks try lubricating the gasket with grease(just a little) instead of oil. If you still have leaks the filter head may be warped.