Running Water and Drain from Slab to Slab

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by bnoji, May 22, 2007.

  1. bnoji

    bnoji New Member

    Messages:
    7
    Location:
    Delaware
    I'm looking for some guidance on running water/drain from the house to a detached garage approximately 35ft away. Both are on slab foundations. It seems the easiest place to tie in is the kitchen cold water and drain as they are both above the slab, directly against the back wall and the nearest water/drain to the garage. I've gathered that I'll need to dig a trench 36" deep and run 1/2" K-copper and 3" PVC under the footings of both the house and garage. The copper will be sheathed in 1" PVC where it contacts the slab.

    I'm unclear about a few things:

    1. How to connect the incoming drain to the existing undersink drain. I've attached a picture of what it looks like under the sink:

    [​IMG]

    ETA: The blue valve is for a silcock on the back of the house. I assume I will need a sump to make use of the kitchen drain?

    2. The best way to excavate and fish the lines through the fill between the slab and the bottom of the footings.

    I considered breaking up a 2'x2' square in each slab, working from the inside and finishing with bag concrete. If there were a way to do it from the outside (and not have to break up the floor) I'm open to suggestions.

    I paid a plumber to do an estimate. He said it would be several thousand and if I don't mind the digging I could do it myself in a weekend and save on most of that. I'm comfortable doing all the labor involved, but not the planning/design.
    Last edited: May 22, 2007
  2. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    Naturally, you cannot connect to the kitchen drain above ground. Round number, you will need about about 9 inches of drop on the drain line as it runs from the outbuilding to the house. You will need to jack into the slab under the kitchen or somewhere to tie that in.
  3. kordts

    kordts In the Trades

    Messages:
    551
    Location:
    exurban Chicago
    What fixtures are being installed? That small of pipe and that distance might be a no-no.
  4. bnoji

    bnoji New Member

    Messages:
    7
    Location:
    Delaware
    The only fixture in the garage will be a utility sink.

    So you're saying I need to dig 36" on the garage side and approximately 45" on the house side in order to maintain that slope at a proper depth? What drain would I tie into that I would find at that depth?

    I was told a pump would allow me to drain a sink from a lower area to a higher area. Maybe something like this: http://www.femyers.com/Products/sse/sse_ed25.html
  5. bnoji

    bnoji New Member

    Messages:
    7
    Location:
    Delaware
    I took a few more pictures this morning and tried to sketch out the existing drain locations in case it may help. Please excuse the embarassing mess in the yard...the house was left to us with "some work" to be done and I'm right in the middle of it all.

    I mapped out all the drains in the house:
    [​IMG]

    Looking at garage (from silcock on back wall, directly in front of sink):
    [​IMG]

    Looking at the house:
    [​IMG]
  6. bnoji

    bnoji New Member

    Messages:
    7
    Location:
    Delaware
    It looks like all the drains in the house lead to the bathroom. Unfortunately, the bathroom is the only room in the entire house where I can't break the floor because of the new tile (and it's our only bathroom).

    While following the drain lines I noticed that there is no slab under the tub (not just the drain, but the entire tub). Is this normal?

    The other issue I'm having is with the slope of the drain. Assuming the main sewer line is 12-16" below the house slab, maintaining a downward slope would require me to go through the footings of both buildings. This opens up a whole new line of questioning....

    1. Does the drain line need to be below the frost line as well?
    2. Is it acceptable to go through the footings rather than under?
    3. For the supply lines to the garage, can I use a conduit bender and torch to make a continuous "L" and avoid the 90 degree joint under the slab?

    I have plenty more questions, but I'm not so sure I'll be able to do this the right way. Thanks for the help so far.
  7. Pewterpower

    Pewterpower New Member

    Messages:
    262
    Location:
    Tampa
    If it's just a utility sink, I'd just run the drain line thru the wall and out onto the ground, or maybe a drain tile.
  8. bnoji

    bnoji New Member

    Messages:
    7
    Location:
    Delaware
    The garage sits in a low spot and I already have some drainage issues. The previous owner never installed gutters on the 20 year old garage (and removed them from the house years ago).

    I'm not even sure if I'll be able to excavate for the supply line on the garage end. Last time I tried I made it 30 inches down and my hole started filling quickly through the footings (from the inside out).

    Right now I have a hole in the garage wall bridged by a piece of 1/2" copper and a silcock on each side of the wall. When I need water, I roll out a garden hose, connect it to the outer silcock, turn on the outside valves, drain into a 5 gal and carry it up the hill in the background when it's full.
  9. toolaholic

    toolaholic General Contractor Carpenter

    Messages:
    874
    Location:
    Marin Co. Ca.
    Let's Cut To The Chase

    #1 We have no idea how many units are coming in from the garage.
    #2 Are You thinking of dumping them into an 1 1/2" waste line??
    #3 It's obvious ,by your questions, You are in no way qualified to attempt this job? Suggest You hire a plumbing cont.
  10. bnoji

    bnoji New Member

    Messages:
    7
    Location:
    Delaware
    As I said, the only fixture draining into this is a utility sink in the garage.

    Why not? The water being drained is clean (not grey/black) and at a rate far less than an average sink or clothes washer. The question was how and where to do it.

    I already stated I was not experienced and that I paid a plumber for an estimate. He told me I could do this myself over a weekend and they would end up charging me several thousand.

    Running the supply line is no problem. With a ditch witch, we'll have that done in under 2 hours. I'm really only looking for suggestions on options for running the drain lines because breaking the slab over the drains (bathroom floor) is not an option.
    Last edited: May 24, 2007
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