Actually a 'flush' in an 03 Ody is 4 drain and fills. It's in the owner's manual, page 308.
"Do this three times. Then drain and refill the transmission a final time." 3 + 1 = 4
If you have it done at a Dealer, I believe they do it all while its on the lift and just go through all the gears and TC lockup while it's up there. Quicker, but not really better. Time is money!!
If your fluid was pretty dirty, do the 2nd one shortly after the 1st and around 10 miles or so, being sure to go into TC lockup and all gears including Reverse.
If it now looks pretty clean, do the next two in about 100 mile increments to allow the new additives in the atf to 'slowly' dissolve the varnish type buildup in the tranny. At least that is what a lot of people in here suggested. Makes sense to me.
I believe the amt of fluid it takes to go from the low mark to the full mark is 8 oz. A slight (1/8-1/4") overfill is not going to hurt anything.
BTW, many on here recommend doing a single drain and fill every 30k or so AFTER you get the fluid looking good.
Buffalo4
PS: Number of drain and fills and % of new fluid: 3 1/2qt/drain and fill: 42,66,81,89 ----14 qts total.
PPS: BTW, I just use the Valvoline MaxLife Dex/Merc atf and think it does great!