Installing basement slop sink questions part 1

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by giantsean, Jun 1, 2021.

  1. giantsean

    giantsean Member

    Joined:
    Mar 3, 2015
    Location:
    Connecticut
    Hi All,

    I have an old cast iron farmhouse sink that aside from being strong and useful, is way too big. I had acquired a stainless steel double basin sink which is much more workable and was working on installing.

    I am trying to work w/ existing plumbing and had some questions. The existing setup is dead wrong and I am trying to take it one step at a time. The washer empties into the waste pipe of an old kitchen sink (since removed) directly into the sewer pipe, and has no trap. I understand the "santee on it's back" that it's built on top of is wrong, and will correct that down the line.

    For now I'm trying to replicate this pic, which I think will be fairly straightforward, and top the vent w/ an AAV. The trouble is that the santee that the old sink emptied into is pretty high off the ground in relation to the current sink. Can the sink drain level be at or only slightly above the trap arm? (obviously it will back up if it's lower). Either way I'll probably have to mount the sink up a little higher, but any higher and it will be too high to use.

    The other question in this setup is that can this contraption take a horizontal 90 before it empties into the sewer pipe?

    Many more questions but I'll take it a few at a time :)

    Thanks!

    20210530_194351.jpg 20210530_194550.jpg trap plan.jpg
     
  2. Tuttles Revenge

    Tuttles Revenge In the Trades

    Joined:
    Oct 15, 2014
    The way to get your trap as low as possible is to install a Wye to the downslope/right of the existing tee just a few degrees above level. Then a 45 elbow to bring the two pipes parralel to each other. That is your drain connection to the 3 or 4" drain we see. The reason you want to bring the wye up off of horizontal is that when waste comes down that main it will flood about 1/3 of the bottom of the pipe.. so the wye is connected on the Invert/upper portion of the drain where its not flooded at every flush upstream. Next would be a combie/wye take off that is vertical for the vent then your trap which would receive the waste as your illustration shows.
    Slop Sink.png
     
    Last edited: Jun 1, 2021
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  4. giantsean

    giantsean Member

    Joined:
    Mar 3, 2015
    Location:
    Connecticut
    Thank you! In that case it sounds like I am attaching the wye inline w/ the 4" sewer pipe? For a few different reasons I'm trying to avoid cutting into that pipe for a while, hence trying to make the existing setup work as well as possible. But I get that it's not right (and never will be, if only for that sani-tee on it's back). End of the day if I cut into the 4" I might as well try to drain it directly into the line behind the sink.

    With the 1.5" sani-tee as it is now, is there any risk of water sloshing from the 4" up into the 1.5" tee, or is it unlikely?

    Finally, if I read you right, with the wye angled up a few degrees, the sink/washer waste pipe will be parallel but very slightly higher off the floor than the 4" sewer line, correct? But that will still be below the 1.5" sani-tee as it sits now.
     
  5. Tuttles Revenge

    Tuttles Revenge In the Trades

    Joined:
    Oct 15, 2014
    Yes. Angling the wye slightly prevents the waste from the 4" to not flood into the 2" every time a toilet is flushed. But having the connection off to the side and basically at the same plane as the 4" allows the lowest height for the trap and the longest possible stand pipe for the clothes washer and the greatest possible distance between the connection of the sink Tee and the trap. The only downside is that you will have to spend an extra 15 minutes installing the Wye and a few extra fittings to reconnect the vent. The upsides are that the installation will be optimal, you will never have to touch it again.

    On the other hand I would predict that the existing connection will cause backups into the sink as the clothes washer pumps more than the 1.5" drain can handle. The potential back ups will be absorbed by the slop sink so no real flood issues. But maybe it would work just fine.. But since I've never had the opportunity to install anything in that manner, I have no direct experience with it.

    There is zero chance of waste Sloshing up into the san tee on that horizontal run. The waste will have settled down from its drop by the time it passes by the tee.

    As far as the diagram.. think of the trap is filled with water to the height of the bottom of the trap arm pipe. Water from the sink will drain into that trap as long as it is above the trap arm height. basic physics. But as water is being pumped from the clothes washer some could fill back into that horizontal drain and into the sink.
     
  6. giantsean

    giantsean Member

    Joined:
    Mar 3, 2015
    Location:
    Connecticut
    Thank you again... this is great info! So interestingly to the above, the drains for the old cast iron sink hooked into that 1.5" sani-tee w/ no ill effect for going on 30+ years now (ever since my dad took it upon himself to hook us up to city sewer, digging a 15' hole himself in the yard rather than pay someone to do it, and ultimately plumbing it wrong lol... RIP to the GOAT :p). Anyway, backups have never been a problem with this particular setup... proof positive that things may be "wrong" but still work great lol. That washer is now a backup to one upstairs and used so little that if not for the sink I would probably have to fill the trap manually when it dried out every so often.

    I really like the wye idea and will look to make that work once I get everything situated. Thank you again!
     
  7. Tuttles Revenge

    Tuttles Revenge In the Trades

    Joined:
    Oct 15, 2014
    I lived in a house with every single plumbing item installed exactly the Wrong way.. everything.. While it all "worked" there were a few things that simply worked wrong without being noticed until it got worse. There are many plumbing codes across the US and each of them has ways of doing things that are correct in one state or county.. but totally Wrong in the next. And like how laws are passed generally at the local level, each area is an experiment in trial and error. Which hopefully we learn from them and move forward by using best practices rather than always sticking with tradition
     
    giantsean likes this.
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