Because sealant is designed to clog holes, the sealant can often clog up the air valve and cause air to leak out or make it difficult to add air in. The best way is to remove the valve core with a valve core removal tool or, in a pinch, a set of small pliers can be used to unscrew it. A thin object such as a toothpick or nail can then be inserted to clear the valve out of sealant. If sealant is clogging your valves often, it is sometimes best to replace them occasionally.