my small camelback is 7 years old and my larger hydrapack is about 5. I keep the bladders in the freezer when not in use. I heard this keeps bacteria from growing. Also, every six months I put some water, baking soda and uncooked rice in it. I shake it up and this does a good job of cleaning/de-scenting it. The rice really scrubs the liner without damaging it. I use mine all year for mountain biking, hiking and fishing. You could probably give em 1 good cleaning a year if you only use it for hunting. I'll keep doing this till I can't get the stink out.