Firstly I use an injector that goes through (not in) the valve and I've had no trouble injecting the sealant. The suggestion not to shake the bottle but to gently rotate it is helpful. This product cannot seal Rene Herse tires (thin resilient sidewalls notorious for leaks) with old sidewall leaks. Also picked up a bacon fork without incident. No dirtier than other sealants and ideal for flexible (leaky sidewall) tires.