Bicycle tire sealants are basically a set it and forget it solution to flat tires on your bike. You simply fill the tube with a measured amount of sealant, re-inflate it and move on. The sealant automatically spreads out inside the tube to coat the entire outer surface. If (or more likely when) something punctures the tire and tube, the sealant is forced into the hole and plugs it, keeping any more air from escaping.
Well, that’s how it works in theory. It’s not a 100% perfect system, but I’ve still found it to be highly effective at preventing flat tires.
Orange Seal Endurance Tubeless Sealant
Slime Tire Sealer Slime Tubeless Pro UST 6/BX Repair Kit, 8-Ounce
OrangeSealCycling Tubeless Tire Sealant, 32-Ounce
Stan’s No Tubes Tubless Tire Sealant 2-Pack of 2oz Bottles Enough for 2 MTB Tires.
Effetto Mariposa Caffelatex Tire Sealant