Originally Posted by
Barry2
Remove the core from the Valve stem and give it a clean.
At times the sealant gets boogers in the valve seat and they don't seal so well.
Run it under the tap and go at it with somebody else's toothbrush.
Then replace it in the valve stem and tighten.
Barry
This. You can buy a 10 pack or 12 pack of new valve cores on Amazon for a few bucks… I find that they need to be replaced every now and then in a tubeless set up. Takes just a couple minutes. I do it every now and then, when I notice a problem, when I’m topping up sealant.