clogged drains and, SAND?

Howdy,
We've lived in this house for about 6 months, it's in the Sunset District of San Francisco. The sunset if you don't know, was once sand dunes, all the way to the ocean.
The house was built in 1939, and looks to have the original cast iron drain pipes in the basement.
The house has a center patio. That is, a room in the middle of the house, which is outside. The patio drain / kitchen sink drain were clogged about a month ago. Plungers, et cetera didn't work (I didn't try a snake/auger, haven't bought one yet), but a shop vac in reverse (blow) did work (blew crap all over the ceiling from the kitchen sink drain which is adjacent to the patio). One thing I noticed when clearing out the drain in the patio, there was a bunch of what looked like beach sand backing out of the drain.
Now, our shower and bathtub are clogged. The shower drain was starting to slow down, I decided to plunge it last night, and that maneuver only made things worse. Now, both the shower and tub are completely clogged, and not draining, and again, I've got sand coming up from the drains. I've tried having my girlfriend hold one plunger in the tub while I plunge the shower and vise versa, but to no avail. I'm going to try my shop vac method tonight. If that doesn't work, a snake. Unless someone tells me using a shop vac for this is bad for some reason. It really surprised me when it worked.
I'm wondering if anyone has ever heard of beach sand getting in the drain pipes of a house. How could it get there? Is it backing up from the city sewer, or coming in from the vents? If from the vents, which are simply open at the top, is there anything I can do to stop the sand from blowing in? Could the sand be the cause of my drain problems?
Thanks very much, John
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clipped

that we have one, I would get with the city first. Entirely possible that the city side of the line is broken. If it is, they fix it. If not, you know the problem is on your side. Over time, it seems a slow running line could accumulate sand from laundry and house cleaning, although I've never had it happen. Our city has had lots of trouble, and are replacing main sewer lines and pumps in our neighborhood. The problem has impacted our neighbors, with repeated backups, but not us. Mebbe neighbors have bad sewer lines on their side of the sewer, as their drainage is bad as well.
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maybe the watersupply. I put in a main water filter with the clear casing so you can see the filter , i was suprised at all the junk in the water
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John Emery wrote: <SNIP>

Better chance is that there is a fracture in the line underground. That can allow soil/sand to wash back into the pipe over time. A snake is usually ineffective with this kind of clog as the sand simply closes back over the snake. The ShopVac may be better as is pressure sewer cleaning equip.
Try and get it cleaned for now, but you may wish to have the line video taped to look for the cause.
As suggested, ask the city for any relief/advice they might offer.
Jim
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I'm gonna take a shot at this as well, John. Before I used the Shop Vac to blow out the mess, I'd try to use it and remove it. Since you know you've got sand in there, adding pressure to it will only cause it to compact tighter - especially since it's already wet and probably has adhered to soap scum, kitchen grease, etc. If there is anyway you could take a garden hose up on the roof and lower it down to below where the outlet for the kitchen sink drain is - I would try that and see if it helped float and move the sand out. Have your girlfriend keep an eye on the sink and be sure you're not filling it up from the roof. I'm curious why the drain in the patio area is tied to your sanitary sewer? (if it is). If that's the case - that could be your culprit. These drains are normally connect to a storm sewer or drain out at a lower point somewhere away from the structure. Speedy Jim may (unfortunately) be on the money with his assumption of a broken pipe. Considering the age of the building, a soft sand foundation, some settling may have occurred and cracked the old cast iron.
However, the only way to get rid of the sand is going to be either water or pipe removal. Let us know how it works out for you.
Jim

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Thanks to everyone who responded, what a great news group (rather, a great bunch of folks reading / responding)!
Jim, what is it you mean, "take a garden hose up on the roof and lower it down to below where the outlet for the kitchen sink drain is"? Do you mean drop the hose down one of the vent pipes? I guess that must be what you mean.
And as far as the patio drain, what you say makes sense. The patio drain IS definately connected to the sanitary sewer. It seems to me that it shouldn't be, or that it should be separate.
One thing I didn't mention in my original posting is, all / most of the drain pipes in the basement, apart from the large main cast iron pipe going into the concrete slab / floor, appear to be galvanized. That doesn't seem good. Perhaps the sand is coming up, but isn't the real problem?
Well, at this point, the problem seems beyond my ability to fix. Unfortunately, Jim, I didn't get your posting until this morning, and last night, I tried the shop vac method, first in vacuum, then blow, both from the shower, and the tub, while my girlfriend reluctantly held a plunger in either opposite drain. Since, she refuses to shower while standing in mucky pipe water (I did), until I can buy the tools and figure out the problem, et cetera... I sadly had to call a plumber. He's coming to the house this afternoon.
I guess I'll post another question, after I find out more from the plumber, like, "Should I go ahead and replace all the drain pipes" and "Should I have the slab in the basement torn up and the main sewer pipes replaced?" et cetera...
Thanks for your help guys.
John
Jim Mc Namara wrote:

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