I use some of it to grow out macros for the LFS cred, some to grow out brine shrimp on the deck for fish food, and sometimes I use it to kill weeds on a bricked area out back. Problem with using it on the actual lawn is that it remains and will stunt or kill grass for a while. Putting it in storm drains is bad because in my case I am at the top of a hill and the drain empties into puget sound, who knows what problems that could cause. I hatch brine shrimp daily too, so remove tank water to do that and then top off.
This is a great time to grow the brine shrimp out, the weather is good til probably October. I put them in a large fish styro and have a sheet of acrylic to cover it if there is a lot of rain. There are also rotifers in it. Sometimes it gets so thick it's unbelievable. You can paint the outside of the fish box or put it in a cedar frame if the family thinks it's ugly. I use painted fish boxes for planters out front where the sun would beat down on a ceramic one and cook the soil.
Kate