Tufo Tire sealant can repair punctures in tubular cyclocross, road, and gravel tires. Small enough to carry on rides or in the pits at a cyclocross race. Keep some in your toolbox or mechanic's back pocket for emergency mid-race repairs.
In the event of a puncture, remove the presta valve core from the tubular and insert about 1/2 the contents through the valve, then re-install the valve core. Spin the wheel to distribute the sealant, then re-inflate the tire to seal.
You can also use this sealant as a preventative prior to races that have thorns, glass, etc.
Although this product is marketed for Tufo tires, it can also work with other brands as well. Check with your tubular manufacturer if you have any concerns about applying a sealant.