In reply to abr1966:
I’ve just replaced a tyre on my mountain bike, I bought it with tubeless tyres. I had a slash on the side wall, that the sealant couldn’t plug. That’s the first time I’ve known of a puncture in 2 years of riding it, So I highly recommend going tubeless. I had to buy a pump especially for seating the tyres on the rim You’ll need one of these or a compressor. I used gorilla tape to seal the rim and stans sealant. I also bought a syringe that fits the valve, that way you can seat the tyre first then put the sealant in.
Once i’d Pumped it up I was getting air leaking through the spokes but managed to get it to seal by shaking the wheel around until the Sealant plugged it up. It’s pretty simple and well worth doing, there’s loads of YouTube videos to help too