I stopped by the dealer where I bought it and looked at another unit that was in for service, Service writer told me they had same complaint on the trailer that I looked at as I did.
I contacted Keystone and they sent an e-mail stating that the flush valves on the trailer front to back and I quote "Grey, Black, Grey" that means that my trailer and the one in the shop were both labeled wrong.
To confirm I looked at the piping closer this morning and the front is a small drain, center is 3" and the back is small drain.
Problem solved. Looks like Keystone labeler is dyslexic.
Thanks to all for the help
Glenn