Hello everyone! Just joined, hoping I can get some answers from you pros out there :)
So, recently, my shower in my master bedroom has started to back up. It started as a slow drain issue, ended up throwing some draino but no luck. Yesterday I went in and removed the drain cover and gave it a good plunging... started getting what looked like sand coming up. I got a little pile of it and water still would not drain. Today I took the wet-dry vac, stuck it in there, covered it with a wet rag and cleaned out the drain (I could see sand in there before and got a good amount out after). After a while, water no longer backed up.. great, right? Well here is my HUGE concern. My home is single story, concrete slab foundation built in the 60's, So. California, by the way.
1) Why the sand? Is my cast iron, 1960's p trap cracked and that's why I'm getting sand... or dirt?
2) I ran the water, ran out to the front yard where my sewer clean out is located.. looked down with a flashlight and no water was coming through.?

I tested a few other faucets, master bathroom sink, adjoining bathroom next to master bathroom shower, and on both occasions, water can be seen passing through the clean out in the direction of the street to the sewer.
I have no idea how long this has been going on, Im afraid that water has been seeping under my home's foundation for quite a while, is this really, really bad?
If indeed my p trap is cracked and water is leaking, what am I looking at, cost-wise, to get the shower pan removed, concrete cut and p trap changed? It's a small shower, tile on walls, pan for base.
I have a plumber coming tomorrow morning, but I wanted to put this out there to see what you all think or maybe someone had a similar experience. Thank you!

If your cast iron "P" trap is buried in dirt, it could have indeed corroded through. I would have thought, however, that you would have seen water seepage along the foundation if water has been leaking for that long. As far as cost, pretty hard to tell but with the construction details of a tile wall, it won't be cheap. Let the first plumber check, they can run a camera down. Then get competitive bids from others based on the information you have.

Thank you, yeah, Im here waiting for the plumber, hopefully he can give figure it out. Its weird because this morning I checked the p trap and it still has water... so if it had a crack, it would be dry, right? I cant imagine that there is a secondary sewer pipe that only this shower would drain to. I would have thought the same about seeing seepage through the foundation but I haven't. Well, Ill update once the plumber gets here and we try to figure it out. Thanks!

OK, plumber came, checked it out, snaked it and voilà! I can now see water flowing nicely through the clean out. He said it probably still had some blockage and was actually flowing, just really slow and since the bathroom is on the other end of the house than the clean out, it just seemed like it wasn't flowing. And the sand? Said it was probably just dirt build up... man! That must have been years and years of dirt! We have only been at this house for a little more than a year so I blame the previous owners! :) Ok, all is good now, I feel so relieved! Glad I found this site, there is a lot of good info on here, going to definitely bookmark this one! Thanks!

Good news for you! Shower drains, for whatever reason, probably flow, tend to clog up with precipitated salts from hard water and soap. I just pulled a shower drain cover off and the drain was constricted with a white mineral deposit. The drain hole was only 3/4". Chiseled it out, flushed it and it ran great. Used to build up 1" water and slowly drain.