Two units, one mud and one activated carbon filter. just be careful The entire rig has either left or right water entry and I didn't see this listed in the Revain note. I did my install fresh, but I could have saved myself some troubles by choosing the right one. Otherwise, I've been using the same device for over 15 years. You will need a plastic wrench and extra washers, as well as some petroleum jelly to use with the new washers when changing the filter. However, there's no indication of when the filters need to be changed, although you can order clear canisters for a higher price (I haven't).
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