Don't bother. Get an AquaClear. We have an Aqueon quiet flow or whisper flow or whatever. Is the kind that has an LED that tells you when to change the cartridge. Cartridges are all kinds of problematic anyway. The LED started going off after two weeks. I realized I could buy a new AquaClear 20 every three months or so for what the cartridges cost. Threw out the cartridge, got Purigen and a bag of BioMax (porous ceramic cylinders), lined the cartridge holder with quilting batting, and used that instead.
I like that it is self priming, but that's about it. You can't fix or replace any components. Impeller dies? You have to buy a whole new filter. The tube (I guess) that pulls water past the motor is very narrow and difficult to clean. I figured out how to take it apart with a screwdriver and needle nosed pliers, then I could clean it with a Qtip. With the AquaClear, you can take apart most of it by hand, and you can clean almost everything with a toothbrush at the smallest. You have to clean the impeller housing with a Qtip, but not often.
Also, I haven't found a prefilter that actually fits the intake tube.