DIAGNOSIS You're either cooking very fatty foods without the drip tray liner, or the tray itself is misaligned or blocked. The design relies on a disposable foil liner to catch most of the grease.
FIX First, always use the disposable foil liners made for the Q-Series. They're cheap and save a ton of cleanup. Slide a fresh liner into the metal holder under the grill. Make sure it's seated flat and fully covers the bottom. Second, check that the metal drip tray holder is pushed all the way into its slot—it should click into place. If it's even slightly out, grease will bypass it and run down the legs.
IF THAT DIDN'T WORK You might be overloading the grill. The Q1200 has a finite grease management capacity. If you're grilling a large batch of very fatty sausages or burgers, the sheer volume of grease can overwhelm the tray. In that case, drain or blot some fat from the patties before cooking, or cook in smaller batches and empty the tray liner midway.
HEADS UP Never let the grease tray overflow onto the ground or patio. It's a major fire hazard and can attract animals. Check and replace the liner regularly, especially after high-fat cooking sessions.