Howdy. I've done some plumbing repairs to the faucets and sinks,etc without issue... but I am having a problem with a recently moved-into house. We have dual sinks in our children's bathroom, and both sinks are starting to contain water that slowly drains (overnight empty in the sink). Filling up one sink, causes the other sink to rise. Both drain pipes go into the wall separately. The commode and the tub do not have any backup issues. The 2 sink drain pipes go down an outside wall and then I am assuming under the slab... the house is 1971, and word has it that the pipes are cast iron under the slabs. Neighbors a few years ago had to drill through the middle of the slab/foundation to repair... ouch. I'm worried a bit. Thanks for any info.

Sounds like a simple clog in the horizontal line in the wall tome.
Remove the "J" bend from the trap and send a snake up into the wall, (see image) You'll run into a bend about 8 inches in but once around that you'll only have about 6 more feet to put out. After, flush with a tub of hot water.
Good luck, Tom

Ended up running a snake down the vent from the roof, but took 22 feet of my 25 feet (about 13 feet past the Y in the wall), before the clog was freed up. Appreciate the info!

Thanks for the update. Glad you're all fixed up. Regards, Tom