Appendix D of the manual: this appears to be Channel 23 for the repeater split frequencies (according to the manual, channel 1 is 462.5625 simplex a/k/a FRS Channel 1).
You can change the display to Frequency instead of Channel to confirm the correct frequencies (Menu items 21 and 22).
To clarify, if you enter a DPL, you do not have to enter a CTCSS; they are mutually exclusive.
RT725 gets pretty raunchy, and I assume that this new 550 will be likewise, so don't have children around when you listen.
RT725 was the first GMRS repeater I ever listened to, and I incorrectly concluded that GMRS was the same as CB radio! hahaha