Here is a copy from a 2014 306 - not sure if the layout changed for 2021s. There are also diagrams for washdown, livewell, discharge and freshwater systems in the 2014 manual if it appears to match your boat.
There aren't and that was a surprise to me. In addition I had to fill in a zillion fields to get to the download. I really dislike the way Grady now manages the manual site.