I unroll one of those blue hoses to the middle of the side yard and let the backwash go in to the grass. It's a little sloped, so a lot of the water ends up on the street and heading for the stormdrain, but some will soak in and it shouldn't hurt the grass.
I also use Fiberclear as it's supposed to be a little more environmentally friendly and it requires less in the filter.
In some jurisdictions, a DE filter has to be backwashed into a "settling tank" to keep the apparently terribly dangerous DE from getting out into the world at large. Your local water authority probably has regs/guidelines that you can look up. Obviously most of us don't think that DE in the environment is a particular problem.
I piped mine about 40', silghtly up hill and away from my equipment since it would run down hill andagainst my neighbors home :-0 I now let it go into the woods that are behind their house. If they ever clear their back yard I suppose I will have to go another 80' to let it reach the street behind our home.