I own a rental property that has a basement with a laundry sink, and I am
wondering if there is such a thing as a drain line backflow preventer that I
can install in the laundry sink drain line to prevent sewage from backing up
into the sink and overflowing onto the basement floor.
The idea would be to prevent sewage from backing up into the basement if the
main sewer line ever gets clogged (which has happened a couple of times in
the past). My thinking is that if I can prevent any backup through the
laundry sink drain, then any sewer clogs in the future will just overflow at
the curb vent by the street in front of the building -- and will not back up
into the basement.
When I do Google searches for sewer backflow preventers, all I see are
devices that are for a 4-inch main sewer line. Here's a YouTube video
example of one type of 4-inch backflow preventer that I see online:
But that is not what I want or need. All I would really need for this
application is a backflow preventer for the laundry sink which has a 2-inch
Does anyone know of a drain line backflow preventer that is made for a sink
drain such as a laundry sink?
Those common check valves are used on water SUPPLY lines, not waste
lines. They are designed to open with some
reasonable amount of water
pressure which isn't likely going to exist in a waste water line,
unless it has a lot of head. I would also expect that even if
it did partially open it would get clogged before long.
Here's a link to one source for 2" waste backflow valves:
That's very true. In most cases, sewers backup very slowly. And as the
water moves the wrong way, the flap in a check valve, allows water to
leak by. It happened to my a few years back. When I went to the
basement, the laundry tub was full, almost to the top and showed no
signs of stopping ... although its rise was very slow. I took a garden
hose, attached it to the faucet and put the other end in the sump. The
faucet was turned on, and when the water started flowing into the sump,
I removed the hose end from the faucet, with the water still running. I
then plunged it into the almost full sink. A siphon was started, which
removed most of the water from the sink. At this point, the pressure
differential across the check valve was high enough to keep the flap
sealed and no more water came in. BTW, a 2" ball valve could be used to
close the drain line, but of course, it is manual.
I was thinking of that idea before it dawned on me that there may be an
automatic back flow preventer that I could use instead. When I was thinking
of the ball valve, my thought was that the tenant who uses the basement
almost never uses the laundry sink. However, the washer does empty into the
sink. So, I thought that maybe I could set the washer up to empty directly
into the sewer line up high (not via the sink) at a location that is above
the curb vent level out front. I would of course need the washer to empty
through a trap first to prevent sewer gases from backing up into the
basement. Then, I thought I could put a 2 inch ball valve in the sink drain
line and tell the tenant to only open that when using the sink, and then
close it when done. He is motivated to do that because he actually does use
the basement area and has experienced the sewer backups into the laundry
sink and then onto the floor in the past..
Thanks. The 2 inch backwater valve may be something that would work. I
can't quite tell from the website exactly how it works -- meaning what the
internal mechanism is. Maybe I can check one out in person at a local
plumbing supply place that I use and see the internal mechanism etc. I'll
bring a printout from the link you provided so they'll know what I am
YOu will probably get more information if you use the term BackWater
Here is one that offers it in 2" - no affiliation!!! :
I wonder whether you have done a thought experiment to ask what will
happen if the laundry sink doesn't overflow. If you eliminate the
pressure relief that the drain line gets from the laundry sink, is it
going to overflow somewhere else instead?
Interesting question. I was all set to write back how my plan is designed
so that if there is a backup the overflow will come out of the curb vent and
won't back up into the laundry sink and basement.
But then it dawned on me -- duh -- what if the blockage is in the main line
before the curb vent? In that case, the backup would be into the 1st floor
apartment tub and toilet and then, of course, would overflow into the 1st
floor apartment. That has me wondering if there is some other plan that I
could figure out.
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