Using Automotive Antifreeze in Black Grey Water Drains

But Jim, we're answering the OP's question. If you need to comment on someone else's replies, you need to point that out. I agree with you, the stuff will eventually end up in the gray/black tanks and then into a sewer some place.

But the fact remains, the OP was asking about drains...in his title he indicates black and gray water drains but his last sentence specifies only gray water drains. In either case, the operative word is "drains".

Ron