Dave,
On our '05 2955rl the vanity sink does drain into the grey water tank. I know this for sure since when I want to clean flush my grey water tank I fill it using the vanity sink.
This may well differ between models.
Tom
Tom & Nancy
TV: 2005 Silverado HD-2500 Crew-cab Duramax/Allison
5er: 2005 2955rl
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