I'm adding a sink in my basement. The basement is already prepped
with an available 3" drain pipe in the floor.
Since the sink drain is at the lowest point in the house, I'm
concerned that if the sewer ever backs up that the sewage will come up
out of the sink and into the basement. So, I'd like to put either a
ball valve or a check valve on the pvc drain pipe to prevent back-
flow. Is this done at all? If so, what can anyone recommend. The
drain is 1.5" but the floor currently has a 3" drain pipe. So, I
guess I'll need some type of adapter to do that as well. Any advice
on that would be appreciated too.
PVC ball valves readily available. Will it be remembered to close?
If you can put a horizontal run in, put a check valve like used
for sump pump.
Neither of these are commonly used on waste lines.
Is there a floor drain anywhere in the basement?
If so, that probably connects to the san sewer and would be
a much bigger threat.
I have both a ball valve and a check
valve .... why? The check valve will
fail when the water rises very slowly.
Once the water is above the level of
the check valve, the flap has no
pressure on the sewer side and thus it keeps
leaking, i.e. the same pressure on both
sides of the flap. I had this happen
a few years ago when we had a huge major
rain, like 23" in 36 hours. .
Even though it is illegal to put storm
water into the sewers, it happens, both
intentionally and non-intentionally.
Anyway, when I went to the basement,
at 3AM (a call from a neighbor), the
water was almost to the top of the sink.
I immediately started a siphon to the
sump. Once the sink was close to empty,
there was sufficient pressure difference
between the 2 sides of the flap, and the
flap shut tight .... no more water in
the sink. This caused me to put in the ball
valve. Have I ever closed it since?
No. These storms seem to come about
every 8-10 years. BTW, my floor drain
DOES go in the sanitary sewer, but
was stopped with a rubber compression
stopper. The sewer lines under the
floor are all cast iron, so there should
be minimum seeping at the joints
compared to the older clay tile pipes.
I complained to the town and they, not
at my expense, put in an anti-backflow
unit in my front lawn. It is a sort-of
check valve, but is operated by a float
which pushes on the flap using a
parallelogram arm. If I keep flushing or
running water down the drain, when the
valve is closed, the sewage is then
pumped, ah, forced, into the sewer line
on the street side of the valve. To
my knowledge it has never closed since
it was installed about 10 years ago.
You're very lucky. A relative of mine lived in an area that had a
major flood in the late 90's, and their entire (finished) basement
flooded because the storm sewers backed up and somehow also backed up
the sanitary sewers. I heard they are connected in some manner in
order to handle flooding. (so much for poor design). Anyhow, the
entire basement was full of filthy sewerage and everything was ruined.
All the sheetrock walls had to be removed and all furniture and
carpeting was wrecked. They had around $50,000 damage and their
insurance did not cover it because it was flooding. They took the
city to court (along with many other people in that city). They got
nothing because the city stated that they needed a backflow valve to
prevent the sewerage from entering the house. After the court case
they had this valve installed at a cost of $18,000, and THEY had to
pay for it. Of course the city is always right in the eyes of the law
I'm currently using the thin wall PVC for the drain from the sink to
the floor drain. It's that thinner walled stuff you see iat Home
Depot that is used for P-traps and other sink drain stuff.
The ball valve I want to get is slip-slip and appears to be schedule
40 PVC. Is it OK to glue the schedule 40 PVC to the thinner walled
stuff that I'm currently using for the drain?
firstname.lastname@example.org ( email@example.com) writes:
| Ut oh. Looks like the 1.5" schedule 40 stuff and the 1.5" tubular PVC
| for the sink are different in size. !! Dammit. What do I need to
| do here?
There are "adapters" in the sense that you can get a PVC fitting with
cement or threaded schedule 40 on one end and a compression (slip) ring
for the tubular on the other end. This would normally be used where
the trap tubing connects to the house drain plumbing (or where the
tail piece connects to a schedule 40 trap). You can also get Fernco
couplers to go between tubular and other pipe types. You probably
don't want to transition twice so try to use schedule 40 for everything
after the valve.
Yes, I was lucky. The city, at the
time, owned 1/2 of the sewer system
in town, the other 1/2, owned by a
corporation. The city had some kind of
a crazy agreement with that company,
that anyone who needed an anti
backflow valve would get it, even if
they were on the city system. I saw the
bill, it was $5K, which I think was
cheep at the time, 10 years ago. I
probably don't need the system any more
because the city put in a larger
lift station, which is located about 2
block away. It's got 3 huge pumps
powered by several different
substations. I don't think they ever
The OP might be better off putting in a grinder lift pump. water goes
to a sealed container and gets pumped up high to a existing drain line
above flood level.
will cost more than a valve but is automatic and requires no human
thats means someone will not forget to shut the valve.....
The 3 inch line in your floor is the toilet line for a toilet in the
basement and should have a backup valve on it. The line you are
putting in should go to the line heading for the street or into a
existing drain line in the house. Unless you don't want to add a
toilet downstairs suggest you make this connection changeble in the
future. Remember much easier to do right once than twice wrong. If you
connect to this 3 inch above floor and there is no back up you will
have to put one in the line to the drain the cheap sump pump kind
don't cut it.
I am opting for a ball valve because I think it will be more
reliable. The sink will rarely be used so I will just keep the valve
closed all the time except for special occasions when I'm using the
sink (which is in a bar in my basement).
Thanks for your feedback everyone!
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