Best Chemical Drain Cleaner in Raleigh NC

So my tenants called, which my lease states I will not be responsible for outside services, the man came and inspected and said I don't have time to do this now, came back next day and said he could not fix unless he tore up walls and cabinets, so he put $20 shark bite cap on and it still leaked. They wanted $305.92 and didn't repair, turned us, the landlords into collection agency.