if you are talking about salt water it kills grass and taints the area you are dumping due to high salt content I would recommend dumping down the toilet or bathtub should be fine and not harm any plumbing
I drain mine stright into my sink since its right there. Stright back to the ocean after a quick pass through some human waste. I use to drain it in my little yard. Kills the weeds along woth all the pretty flowers.