Rick
Since yours is a 2006 it probably drains into the gray because your toilet is probably facing different than ours. I think that is why they put the sink with the black, they are right next to each other on our unit. The later 2005's had the toilet facing towards the bedroom and that puts the toilet drain away from the bathroom sink. It also gives you more unobstructed room in the basement which is probably why they changed it.
Happy trails........................
Sue and Ed Rowe
Hemet California
2005 3400RL
2006 GMC 3500 Dually, D/A, Crew Cab, Long Bed
