Vanity sink drains into black tank

Yes...all Travel Supreme did that as does Entegra Coach now..they do that so the sides of the tank get washed and more water is put into the tank...some other floor plans had that and you would have to get to manufacturer plans to see if it did..

The Bathroom sink in my Winnebago drains into the black tank.

The idea is that the more water in the black tank, the fewer problems you will have with blockage. Our Sahara has this feature as well.

The bathroom sink in my TT also drains into black. I believe it is to give that tank extra water.

It is NOT to get more water into the black tank. It is because the floorplan design does not leave any room to run that particular sink drain plumbing to the Gray tank, so they route that sink to the black tank. There is NO rule or Law that states ONLY Black Water can go to the Black Tank. Doug

Both my sinks drain into the black, I take long showers.

dougrainer wrote:
It is NOT to get more water into the black tank. It is because the floorplan design does not leave any room to run that particular sink drain plumbing to the Gray tank, so they route that sink to the black tank. There is NO rule or Law that states ONLY Black Water can go to the Black Tank. Doug

Well, the OP said it was an option on his coach, so it appears that at least Mandalay can run the drain to either tank.

My bathroom sink drains in to my black tank at an angle and helps flush away a pile that could form right below the toilet.

Normally, our black tank can go twice as long as our grey. Just for volume alone, your set up makes sense. Add to that the added benefit of having more water to break down the TP and that makes it even better.

Some boon dockers modify their waste plumbing to be able to transfer grey over to black. You got it for free.

It's a good idea. I wish ours did.