(206) 949-5683, Top Rated Plumber, Seattle
Results 1 to 14 of 14

Thread: Connecting two traps together to maintain prime

  1. #1
    DIY Junior Member Brendan Simons's Avatar
    Join Date
    Sep 2013
    Location
    Ontario
    Posts
    6

    Default Connecting two traps together to maintain prime

    I am building a second-floor laundry room. There will be a floor drain under the washing machine, and I'm looking for a solution to keeping water in the floor drain trap without being able to reach it easily for maintenance (and without a trap primer valve, which is proving to be hard to find around here).

    My current thought is to connect the floor drain trap to the trap at the bottom of the laundry standpipe, as shown in the attached sketch. Basically I'll extend the laundry trap depth a bit and install a 1/2" tee below the waterline (but above the trap weir). From there, I'll run a 1/2" pex line down to the floor drain. The laundry trap should drain through the pex line into the floor drain trap until the water level is lower than the tee. I'm hoping that, since the pex line is only 1/2", it won't allow enough flow from the standpipe to flood the 2" floor drain. Can you point out any flaws in the design?
    Name:  laundry trap priming diagram.jpg
Views: 437
Size:  20.1 KB

  2. #2
    In the Trades Tom Sawyer's Avatar
    Join Date
    Nov 2010
    Location
    Maine
    Posts
    2,946

    Default

    The short answer is NO!
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

  3. #3
    DIY Junior Member Brendan Simons's Avatar
    Join Date
    Sep 2013
    Location
    Ontario
    Posts
    6

    Default

    OK... give me the long answer. I'm having a heck of a time finding the "industry standard" way of keeping prime in a floor drain. The local hardware stores don't even sell a trap primer valve.

  4. #4
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    Location
    New England
    Posts
    21,434

    Default

    You can put a T on the fitting into the washing machine, then use a hose with a valve in-line to limit flow, and use that to run some water into the trap each time the WM is used. If you dialed down the flow to a slight trickle, you'd keep the trap primed as long as you did wash on a regular basis and not impact the time it takes to fill the WM.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  5. #5
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    Location
    New England
    Posts
    21,434

    Default

    Go to a plumbing supply store...unfortunately, most of them are not open late or on weekends.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  6. #6
    DIY Junior Member Brendan Simons's Avatar
    Join Date
    Sep 2013
    Location
    Ontario
    Posts
    6

    Default

    Thanks, but must I use fresh water to prime the floor drain? This post from Terry a few years ago suggests something like I drew (unless I misunderstand him). I'm just trying to plan the details.
    Last edited by Brendan Simons; 09-04-2013 at 02:45 PM.

  7. #7
    Forum Admin, Expert Plumber Terry's Avatar
    Join Date
    Aug 2004
    Location
    Bothell, Washington
    Posts
    14,214
    Blog Entries
    1

    Default

    The floor drain would have a p-trap to prevent sewer gas.
    It would need to be vented, and the vent can tie back into the washer vent, at 6" above the flood level of the fixture.
    The floor drain would need a trap primer to keep it wet.
    Two ways to do this are"
    A dedicated trap primer connected to the water supply.
    A tee on the standpipe of the washer that diverts water to the p-trap. Everytime you run a load, a bit of water would wind up at the p-trap from the water being discharged.
    I have done this with a trap primer before.

    The drawing you have shows a floor drain without a vent.
    Everytime the washer discharges, the p-trap of the floor drain will lose water. It may take a day or two before the trap primer would refill the p-trap.
    Put a vent between the floor drain, and where it wyes into the waste line of the washer.

    http://www.terrylove.com/forums/show...from-standpipe
    Last edited by Terry; 09-04-2013 at 04:44 PM.

  8. #8
    DIY Junior Member Brendan Simons's Avatar
    Join Date
    Sep 2013
    Location
    Ontario
    Posts
    6

    Default

    OK, I thought I could get away with wet venting the floor drain, but I'll double check.

    Assuming I add the vent, are you agreeing that the two traps can be connected, or do I have to use a trap primer valve?

  9. #9
    Forum Admin, Expert Plumber Terry's Avatar
    Join Date
    Aug 2004
    Location
    Bothell, Washington
    Posts
    14,214
    Blog Entries
    1

    Default

    OK, I thought I could get away with wet venting the floor drain, but I'll double check.
    Check all you want, but the answer won't change.
    You make ask some homeowners and I'm sure they will give you the green light. Plumbers won't, because they know it's not legal, and even more important, it doesn't work.

    A washer is never allowed for a wet vent. It's a pumped drain that requires 2"
    Even if it could be wet vented, it would require upping the size of the waste line before you could consider it for venting purposes. It would need to be at least a 3" line.

    Here is one way to prime traps





    The blue line going into the slap is for the floor drain. There is also a copper line from the splitter that primes the ABS p-trap.
    Last edited by Terry; 03-04-2014 at 03:14 PM.

  10. #10
    DIY Junior Member Brendan Simons's Avatar
    Join Date
    Sep 2013
    Location
    Ontario
    Posts
    6

    Default

    Cool. I'll add the second vent. What about the tee in the stand pipe?

  11. #11
    Forum Admin, Expert Plumber Terry's Avatar
    Join Date
    Aug 2004
    Location
    Bothell, Washington
    Posts
    14,214
    Blog Entries
    1

    Default

    Cool. I'll add the second vent. What about the tee in the stand pipe?
    I haven't tried that yet. Maybe someone else has.

  12. #12
    DIY Junior Member Brendan Simons's Avatar
    Join Date
    Sep 2013
    Location
    Ontario
    Posts
    6

    Default

    I did a bit more digging. The Ontario Building code (and national plumbing code) Section 7.4.5.5 calls for a trap seal primer or "equally effective means", which isn't very precise. There is an ASSE standard 1044 which governs trap primers connected to "waste line tail pieces from fixtures, such as lavatories, sinks & similar fixtures where grease is not normally generated". I'm not sure a laundry stand-pipe would be acceptable in that standard, and I don't really want to spend $45 to check

    In my digging I also found a *lot* of complaints about fowled or otherwise broken trap primer valves. It would sure be nice to build a system without a mechanical valve.

  13. #13
    Forum Admin, Expert Plumber Terry's Avatar
    Join Date
    Aug 2004
    Location
    Bothell, Washington
    Posts
    14,214
    Blog Entries
    1

    Default

    In my digging I also found a *lot* of complaints about fowled or otherwise broken trap primer valves. It would sure be nice to build a system without a mechanical valve.
    Everything fails at some point. We install them with unions to make replacement easy.

  14. #14
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Location
    Cave Creek, Arizona
    Posts
    25,679

    Default

    Usually it is done using water from a lavatory or toilet with a flush valve. The tap into the drain/riser has an upturned opening so the water will flow into it. The washing machine riser should NOT have "standing" water in it to flow through your tee. There is a BAP fitting which inserts into a 2" line with a 1/2" tap for an adapter. You could use one at both ends of your piece of PEX and enough water should splash into it to maintain the seal.
    Licensed residential and commercial plumber

Similar Threads

  1. Pipe burst! CPVC, to prime or NOT to prime? What went wrong?
    By Sincraft in forum Plumbing Forum, Professional & DIY Advice, Tips & Tricks
    Replies: 10
    Last Post: 02-27-2012, 08:06 PM
  2. Pump Won't Prime or hold prime
    By PAmom1991 in forum Pumps and Tanks Well Forum & Blog
    Replies: 6
    Last Post: 05-31-2011, 07:09 AM
  3. Pump lost prime - won't prime (long post)
    By BWFRJR in forum Pumps and Tanks Well Forum & Blog
    Replies: 2
    Last Post: 08-30-2010, 06:37 PM
  4. How to clean & maintain elec WH tank
    By CHRPC78 in forum Water Heater Forum, Tanks
    Replies: 1
    Last Post: 02-26-2010, 07:21 AM
  5. Best way to maintain a 15 year old toilet
    By jigarlakhani in forum Toilet Forum discussions
    Replies: 0
    Last Post: 03-16-2006, 04:20 PM

Tags for this Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •