Its always bugged me that our lift pumps don't have a manual primer. I like a pump that is driven by a diesel engine, not a little electric motor. My 85 Mercedes had one, which made priming after a filter change or opening up the lines a breeze. Fortunately, the little 6 banger going in my 97 has a manual primer button as well. The mechanical lift pump on our engines acts as a valve, and won't allow fuel to pass - so its not as simple as adding a boat or filter head primer, unless you don't have a mechanical lift pump.