I just bought a 1980's condo, and there is no p-trap under the kitchen sink. The drain is down into the slab. It's a 50/50 sink with a disposal on the left. Is a p-trap still needed with this vertical drain? Thank you.
If there is already a trap underground, you won't need a trap under the sink - indeed if you added one, you will have major problems with draining with a double-trapped setup.