I've had my Triumph w Yamaha 150 since 2006 and this is what I do: Since the engine has a flush adapter and your water source has enough pressure to cause a stream of water to discharge from the cowling drain (pee hole), then it is fine to run the engine on the flush adapter only, but it's limited to 1500 RPM max and no longer than 15 minutes. This also ensures adequate water for water pump lubrication. If the overheat horn sounds or you cannot get enough pressure for water to flow from the cowling drain hole, you are required to use BOTH the flush adapter and a lower unit flush adapter simultaneously. Additionally, you should never start the engine out of the water until you have allowed adequate time for the engine block and lower unit to fill with water and start draining out. If water is draining out of the lower unit, it is in fact lubricating the water pump. I know what the owner's manual says, I've also discussed with Yamaha Outboard Engineers. My engine runs like a top since 2006 and I've experience NO problems using this method.