Gray water pit ( bleach or no bleach )
Don’t chemically mess with a gray water drain! 
It is kind of like a septic system and if you kill things eating the little bits of solids it will not last as long! 
Soap scum is a solid in this case if you kill the bacteria it will plug up faster. 
I could take the other side and say you should dump a caustic every now and then to turn the scum into less than scum. But I would not use bleach.