Amazingly enough, automatic dishwasher detergent is supposed to be the best thing to soak cartridges in. Really. There's no specific product that's better. Those here who use it SWEAR by it. You'll need a container or tub big enough to hold it.

I can't tell you how much to use, but I believe the powdered stuff is best. Somebody out there even sells a cylinder that seals that is sized for your system--they suggest you rinse off the cart and seal it in there with water and the detergent--and have two carts. When one gets dirty, you pull out the one in the cylinder, rinse it off, pop it in, and soak the other one...It's supposed to be the easiest way to maintain carts.

I don't promise that this is correct: I have a sand system and the only carts I used were in an EasySet years ago--and they were cheap enough that I could replace them every 2 weeks.

If any cart owner could chime in and either confirm or correct me, it would be appreciated, but the automatic dishwasher detergent has been confirmed from time to time.