Make sure you only use Genuine Honda ATF, if you can't get ahold of some I'd wait until you can.

On a Honda automatic, a very large portion of the fluid won't come out when you drain it, and since it isn't safe or wise to ever do a "flush" on a Hondamatic, it would be best if you did 3 drain & refills with a little driving in between each.

Normally one drain is enough, but if it's been well over 30,000 miles since it was changed, it would be a good idea.

edit: never used the seafoam transmission product, but I'd avoid it just to be safe since the filter on those isn't removable (without a rebuild) whereas on most automatics you'd be able to replace the filter after it gets all plugged up with the crap the seafoam will remove.

I'd look in your owners manual to see if it has instructions, otherwise do a search here and maybe on Google, otherwise you could just pick up a service manual as it will pay for itself over time.