Use sparkly cleaner
Wine is fairly sanitary all by itself - things harmful to people cannot grow in wine (alcohol level 10% or higher). Many winemakers clean and sanitize carboys with a no-rinse product like One Step or PBW. Store cleaned and sanitized carboys mouth down (if possible), or cover the mouth to prevent dust, insects, etc. from entering.
Take a look at the FAQ section. If you search for sanitizing, you'll find that answer.
I've been trying to keep my carboys clean. What do I use to make sure that they're always sparkly?
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