WHY DOES THE WORKER REMOVE THE P TRAP UNDER

WHY DOES THE WORKER REMOVE THE P TRAP UNDER SINK BUT NOT SINK BUT NOT INSTALL A NEW ONE RIGHT INSTEAD HE CONNECTS A STRANGE PIPE WITH AN OPENING EVEN STRANGER HE FEEDS A LONG METAL CABLE DEEP INTO THE DRAIN THE REAL CLOG MAY BE MUCH FARTHER INSIDE FIRST HE PUTS A BUCKET UNDER THE SINK THEN HE LOOSENS THE FITTINGS AND REMOVES THE OLD P TRAP ONCE IT IS YOU CAN ALREADY SEE GREASE AND DIRT INSIDE BUT HE DOES NOT PUT IT BACK INSTEAD HE ATTACHED A TEMPORARY FITTING TO THE DRAIN PIPE IN THE WALL NEXT HE BRINGS OUT A POWER DRAIN CLEANER AND FEEDS THE CABLE INTO THE PIPE AS IT RUNS THE CABLE SPINS AND MOVES FARTHER INSIDE WHEN IT HITS GREASE FOOD OR OTHER BUILDUP IT BREAKS IT APART THAT IS WHEN YOU REALIZE THE SLOW DRAIN MAY NOT BE CAUSED BY THE P TRAP AT ALL THE BLOCKAGE CAN BE DEEPER IN THE PIPE AFTER THE FIRST PASS HE REMOVES THE FITTING A LONGER COIL FARTHER DOWN HE PUSHES AND PULLS IT SEVERAL TIMES TO BRING OUT HAIR AND LARGER DEBRIS ONCE HE PUTS THE P TRAP TIGHTENS EVERY AND CHECKS FOR LEAKS HE FILLS THE SINK WITH WATER AND PULLS THE STOPPER THE WATER THAT BARELY MOVED BEFORE NOW SPINS INTO A STRONG WHIRLPOOL AND DRAINS FAST SO CLEANING THE P TRAP ALONE MAY NOT FIX A SLOW SINK SOMETIMES THE REAL CLOG IS MUCH FARTHER DOWN