if you boil it on the stove for at least 10 minutes it will kill any bacteria or mold that could be in it. let it cool and put out. If you want to be sure your feeders are mold or bacteria free soak them in a bucket with a tblsp of bleach for awhile and then rinse well. and if you think the necter in your feeders outside might be getting stale or comtaminated you can bring it in and boil it and rinse out the feeeders and use it again

I say throw it out and make your own. It's so easy and inexpensive. Use 4 parts water to 1 part sugar. You can used boiled water if you want, but it isn't necessary. Cool it and pour it into a clean feeder (see note above) and hang the feeder and put the rest into the refrigerator. It will last up to 2 weeks. Don't let any mold or fungus grow in or on the feeder because the birds will continue to use it, and it can cause a fatal respiratory disease to the hummer. If you are going to hang feeders then it is a must to keep them clean for the sake of the hummers. And don't add red dye. The feeders attract the hummers just find without adding red dye to the water. Have you ever tasted red dye! UGH!

I live in Rockport Texas where we have the Annual Hummer/Bird Celebration. I'm one of the hummer homes on the tour, and every September I keep about 3 dozen feeders out of varying sizes. At the height of the migration, I am refilling them 3 times a day. I generally go through 50 to 60 pounds of sugar during September, and that's for use for strictly the hummers. However, I do see an occasion oriole and/or anoles taking in the sugar water too.

i agree that making your own nectar is easy and less expensive and i usually make my own. But every year somebody will give me store bought as gift or for birthday. If it has the red dye in it i dilute it down with homemade sugar and water. I boil mine not so much to sanitize the fresh made but to completely dissolve the sugar. if you shake it and don't get it all dissolved it will settle out some. My orioles and tanagers and hummingbirds share the feeders and i purposely drill out the holes on the hummingbird feeders so the orioles can use them easier. the tanagers and orioles poop on the feeders occasionally bust i clean them on a regular basis.
Also i keep a couple spare feeders on hand. i find them often at thrift store or yard sales and use them when i am soaking and cleaning the others. and can rotate that way so there id always feeders out for the birds. Here the season is usually may to sept.