My 2005 Accord owner’s manual says to drain, not flush, the fluid. The pressure fro the flush pump may be high enough to damage the solenoids. Get the engine (transmission, actually) well warmed up and then drain the fluid on a flat surface. You will get at least 70% of the fluid out. Replace the fluid and you are good to go. If you are concerned about the remaining fluid, perform another drain and fill cycle immediately. IIRC, the Honda recommendation is to drain and refill twice (3 fills total) to remove essentially all the old fluid. You can do this easily yourself and don’t need special tools. You will need a narrow ended funnel to fit into the transmission dip stick tube. That is where the fluid is added. The fluid will cost about $24 for 4 quarts.