It's called the BUFO Toad -
http://www.floridagardener.com/critters/BufoMarinus.htm
When Chanel first picked a Toad and dropped it - I called my ER Vet right away and they assured me in Texas our toads aren't toxic - so it depends on WHERE YOU LIVE - The Bufo only lives in certain areas -
You did the best thing flushing his mouth out -
Did the toad run off ? Do you remember what it looked like ? Foaming at the mouth and excessive drooling are signs they touched one- toads excrete a bitter substance & most of the time won't hurt your pet - but a Bufo can kill a dog.
If you don't live in an area that has the Bufo then hopefully he'll be ok
Edited to add - IF you want to be really safe - call the ER vet and ask if
any dogs have been treated for Toad Poisoning recently - they'll tell you if you need to worry or not