I have an old whirlpool fridge model EHT 181ZK ( freezer on top no ice maker or water) On the top of the fridge there is an ice build up and water on the bottom of the fridge. Some water is dripping down the back of the fridge and getting food on the back of the shelves wet. Is this a clogged drain tube? If so how can I fix this? I don't know where the drain tube is?

I believe it is the drain tube. You will need to access the evaporator at the bak of the freezer section. Many times you can pour warm water down it to open if it is a ice blockage. If anything else blocking it you might try a piece of weedeater string and push in it to remove the blockage