You can usually remove grease from a sink drain by mixing a pound of powder detergent with three gallons of boiling water.
Then while the water is boiling slowly pour the boiling water and powder detergent mixture into the sink drain and it will usually heat up the grease enough so that it flows on through.
However if there's too much grease then you'll need to remove the P Trap under the sink drain and clean it out.
Also there could be some grease further down into the sink drain and you'll need to snake the line to remove the grease.
Most times the grease is just clogging the P Trap and simply removing the P Trap under the sink and cleaning it out or replacing it will clear the clog.
Never pour grease down a sink drain or other drain because it can easily clog it.
Always allow the grease to cool down and then put the grease into a container and throw it away.
The boiling water and dish soap will help to emulsify the grease in the drain so that is washes down.