I thought originally you could switch flavors after cleaning but now I know it just seems that the old taste never completely disappears (I've seen where some have said peroxide-ing helps but I hate that smell) so staying in the same family of flavors is a good way to go.
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You can clean them if you want to switch flavors. I think that cartos are cheap enough that I just buy another 10. But yes, you can clean them for that.
But I'm not a big fan of boiling. Seems like for smome flavors, boiling a carto locks in the taste, or sometime, even make the carto taste worse.
It's kinda like the difference of the taste of tea made from boiling water verses the taste of "Sun Tea" made from cold water. To me, using cold water does the same amount of cleaning but with less chance of locking in a taste.
If I'm moving around in the same family of tatses, sometimes I just "phase out a carto. I might have a Pineapple Carto and want to use it for Cheery. I just keep adding Cheery to the Carto every time the carto needs a top off. In 3 or 4 top offs, all you tatse is Cheery. Works going from a light flavor to a stronger flavor.
One thing I have learned is never try something new to all your stuff No Matter How Many People Say It will Work.
So go ahead and try cleaning with 2% Hydrogen Peroxide. Just try it on ONE carto and not your entire supply.
Don't Stress, I'm sure you cartos are fine.