Dave
Very sure. See the post on black tank filling fast. Keystone seems to change things around quite a bit. On the early '05 3400 the toilet drain pipe and the sink drain pipe are only a few inches apart. It makes sense to have them both go into the same tank.
Happy trails..........................
Sue and Ed Rowe
Hemet California
2005 3400RL
2006 GMC 3500 Dually, D/A, Crew Cab, Long Bed