Eheim Pro IIs won't do it. They need the intake and return to be at the same level.
The FX5 will work but you have to prime the system. Once it's started, NP. But getting it started takes a little effort. I used my gravel vac and shoved the hose from the gravel vac into the FX5 intake. Started a syphon then shoved both hoses into the sump. Turn the FX5 on and wait. The FX5 kicks like a mule when it starts. It will run for 2 minutes and shut off to purge air. When it shuts off pull the Gravel vac hose out of the FX5 line without letting the FX5 line get any air in it. Kill the syphon for the gravel vac. When the FX5 kicks itself back on your done.