i always do, dont want any old oil with junk going back into the engine, thats why i change the oil in the first place, to get rid of that crap, use a sucksion gun to get left over oil out of filter, wipe it clean, put filter in then fill the cannister with oil slowly, let the oil flow into filter, that way the engine doesnt hve to wait to long for oil to build pressure at the crank and things, full flow or not it still takes time for the filter to fill