new bathroom addition

[a c]

I am adding a bathroom- basic layout- toilet/tub/vanity, and I am also moving my washing machine to a different part of my house. It would be easiest to plumb everything in to my existing black water sewer line. What are the benefits of keeping the gray/black water seperate? and are there big negatives to running everything to my existing black line? thanks for your input. We are on a septic system.

[jadnashua]

Septic system or city sewer?

[a c]

Septic system. Sorry.