Upon arrival technician found dirty p trap in drain line. Replaced male adapter, tee and p trap to ensure proper drainage. Flushed drain with 28 oz water. Drain line drained properly. Informed customer that it looks like possible sewage issue. Looks like toilet paper on floor drain pan for coil is empty. Offered moisture sensing alarm and/or safe-t-switch customer isn’t interested at this time and will clean up basement/sanitize, will call Plummer/ city if issue reoccurred