This thing is the bomb. It lets you remove old sealant, and inject new sealant with an absolute minimum of mess. A steady hand may be able to get it done with zero drips (The current record in the Pure Gravel office is 2 drips).
The reservoir holds 2 ounces, which is just the right amount for a road or gravel tire.
PRO-TIP: Set a reminder on your phone every time you change your sealant, and keep your tires fresh and juicy.