I change at the end of the season; This was dealer recommended as any contaminates that may be picked up during the season dont sit in the motor during winter storage. I take the boat over to the ramp and just run it on the trailer (crowd permitting) 10-15min to get it to temperature. Then take it home and open the drain & let it sit for a few hours (dealer suggested overnight) I adjust the trailer jack a few times (bow up and down) and seem to get more out that way. There is a measure list imprinted on my disposal container & thats how I judge where to start my refill. Ive never pulled out six quarts, but im also not sure how much remains in filter when its discarded or lines that may not drain.