- A Demented Corner of the North Cascades
I've found that by the time the sealant clogs the valve cores the sealant is substantially dried out and won't plug punctures very well. Usually the performance of slime tubes is best when they are pretty new and gradually deteriorates over time. If you use 'em (and they do have valid uses) you should replace them at least once a year.I bought some slime branded tubes. The valve plugged up after a year and a half. Could not add air when the inevitable 15 psi/6 months leakage happened. Threw them away, use regular tubes and no slime. Knobby tires keep the trash off my tire carcasses.
This is really no different than having to recharge sealant in a tubeless tire.
You can easily remove the valve core on a Slime tube and clean it, though.