Don't use bleach or any store-bought chemicals. I recommend soaking them in boiling water, using a strainer. Vinegar is basically the safest thing for fish other than hot water. Not many commercial window/glass cleaners made out of vinegar do not include ammonia, and those that do are costly.
You can make your own homemade tank glass/gravel cleaner from ½ a cup of ordinary white vinegar dissolved in a ½ gallon of distilled water. I'm sure WalMart or any of those other box stores sell spray bottles, I recommend purchasing one of those if you want to clean the tank walls with the mixture as well. You can soak the gravel in hot water mixed with your vinegar which will most likely get the smell out.
Remember to soak them for a bit afterward to rinse all the vinegar out!
You can make your own homemade tank glass/gravel cleaner from ½ a cup of ordinary white vinegar dissolved in a ½ gallon of distilled water. I'm sure WalMart or any of those other box stores sell spray bottles, I recommend purchasing one of those if you want to clean the tank walls with the mixture as well. You can soak the gravel in hot water mixed with your vinegar which will most likely get the smell out.
Remember to soak them for a bit afterward to rinse all the vinegar out!