I've got a problem where my valve stems keep clogging - I can pump the tyres up OK, but can't let them down at all. It's not the valve itself, as the problem remains if I remove the core. Guessing a kind of flap valve forms at the base of the stem, made out of dried sealant.
A bit of digging (I used an unmounted drill bit) works but soon reoccurs and it's really annoying - I quite like the ability to reduce pressure if I end up doing more bumpy off-road than expected. Any solutions?