I think we had this discussion some time back. We also discussed what was the best products to put in your tank. Sea Foam, Stabil, Lucas, etc.. There are a hundred products on the market. I personnally use Sea Foam. I talked to owner of Sea Foam and he said to put one can in each tank per year. I have my motor services every January without fail. I put a can in each tank everytime I fill them up. Torch has them for 6.99 each. I figure $100.00 worth of Sea Foam is batter than $6000.00 for a power head or something else. Remember, the moter is the most expensive part of the boat.