It’s simple. You take it apart and spray it with a garden hose. If you have a brass hose nozzle to get a hard thin stream then use that. You want to get as much of the residual DE and debris off the grids or tubes depending on the type you have. There will be a lot of gunk up in corners too.

Also, inspect any metal parts inside the filter. Or anything look brown, rusty etc those parts need to be replaced. Look for cracked plastic also.