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Good information was given already.
Rule 1 in sanitizing:
You can only sanitize something that's already clean. IOW, you can't sanitize dirt (or dirty objects).
To clean bottles, you'd need a bottle brush that can scrub the inside, a sink or tub with warm or hot water, and a cleanser/detergent such as washing soda (it's cheap) or (generic) Oxiclean (more expensive).
The most tenacious area for dirt to hide inside bottles is the corner where the bottom meets the side. So pay extra attention to that, make sure the bottle brush' bristles reach into that corner.
When the bottles are clean, rinse out well.
If you have many bottles to rinse, that jet sprayer that was mentioned is amazingly fast and thorough with that. It screws onto a regular faucet, after removing the aerator if it has one.
Then sanitize the bottles right before you're filling them with beer.