well you can have system pressure if an implement/arm/bucket is in the air or under load which will put pressure back on the system until you pull a valve handle to release it back into the tank thru the valve.Best thing to do is stretch out the hoe arm all the way onto the ground with bucket curled out..then with engine off,pull handles on all valves to release any stored pressure energy back to the tank.There's gonna be some leakage,its a hydraulics thing,you can't stop it all but you can catch the majority of it in a pan or 5-gallon bucket.
