I only open my Eheims up about once every 3-4 months to check things out and make sure there's nothing up with the impeller and such. They're probably only cleaned once a year.
Definitely not entering via the spray bar.
Now I'm gonna try sponge layered with a super-fine mesh media bag and filter floss layered with sponge. It's gonna require me to clean the pre-filter more than once per week but maybe this will work.
Typically, sponges keep things down to just 2-3 shrimp in a filter here and there. Not sure what it is with this tank, though. Must be something extra special in the filter that they want to get at.