This picture shows the inside of a p-trap that has been completely blocked up with grease. A blocked drain can happen from years of use and can be easily cleaned by disconnecting the slip nuts on the p-trap itself. It is a nasty job but is an easy one. Many times the problem is right in the trap. When we respond to a kitchen sink stoppage we like to cable the drain from under the kitchen sink. This way if the trap is clogged up we can address it at that time. Many companies have their technicians get on top of the roofs to clear stoppages. When you cable from the roof you also miss the waste arm.