The instructions are quite clear about not injecting this stuff through the valve since it will clog up. But I have read people do inject sealant through the valve. Is the Race Sealant special or going through the valve can work but there is a risk that valve may plug up?
Yes, the Race has larger particles which is more prone to cause issues with valves.
When I inject (regular Stan’s fluid - not the race) through a valve, I remove the valve core first.
Got it. Thanks for the reply. But if I carefully follow their instructions and not use the valve wouldn’t sealant blow back out the valve every time I top off my air pressure prior to riding anyway?
It doesn’t all come spurting out when you add air to a tire. You can even bleed off a pound or two if you add too much air.
You may get a few drops of leakage, but you can limit that by being mindful of the valve orientation/clocking (ie. don’t have it at 6 o’clock). Also, avoid doing it immediately after rotating the wheel where it’s still settling to the bottom).
Excellent points. Again thanks for your input. it will make my switch to tubeless a little easier.
Anytime. Good luck with the conversion.
When I park my bike I leave my valves at 4 or 8 o’clock.
This keeps them above the sealant AND allows any in the valve stem or extension to drain.
I top up with air before moving the bike.
Seems like a ball ache but it’s not, it’s just a habit you get into.
I started doing this after blocking an MTB valve quite quickley. I am on nine months for the road bike now with zero signs that the valves are even getting a little stiff.
WD 
I think the race sealant has chunks of rubber in it… if that is the case I use Truckerco Cream and it is similar to that, i.e. a latex tire sealant with small chunks of rubber. I inject it through my valve stem on my mountain bike when I’m topping it up with no issue.
Link to what I use… big fan of it and its $ compared to Stan’s.
If cost is your concern, you can make your own too. It’s not difficult.
Here’s a snip from a Keith Bontrager interview on YouTube, https://www.youtube.com/watch?v=NpxUcfZhxLk
You can get the latex from Michaels. With a coupon it’s reasonably priced.:
