Problem flowing 4 inch PVC into 3 inch cast iron?

Users who are viewing this thread

skip

New Member
Messages
3
Reaction score
0
Points
0
Looking to see if I've made a mistake here. I've got an old (1920s) house that I added about 30 feet of 4 inch PVC pipe to drain two bathrooms into an existing cast iron drain that goes out to the street. The existing cast iron pipe outer diameter measures 3.3 inches (circumference= 10-3/8). Is this a "3 inch" cast iron drain pipe size?

Is it OK to be flowing from the larger 4 ID to a smaller 3 ID or am I asking for blockages here? I made the connection using a rubber sleeve (with hose clamps) that fit on the cast iron hub OD and the OD of the PVC, so the flow path gets smaller by going through the cast iron hub.

Thanks for your help.
 

Master Plumber Mark

Sensitivity trainer and plumber of mens souls
Messages
5,533
Reaction score
354
Points
83
Location
indianapolis indiana - land of the free, home of
Website
www.weilhammerplumbing.com
its ok

it would have been better if it were 4 inch all the way ,
but you got to do what you got to do,,, thats your
mistake you got to live with.

I doubt the fixture units you have added
will make much difference going into the 3 inch
anyway...

my only advice might be to put some sort of clean out
at where you have to reduce from the 4 down to the
existing 3 inch cast pipe...

makeing the reduction on a verticle drop into the
3 inch pipe might be wiser . ---instead of on a horizontal
Also reduce down with a 3x4 pvc bell reducer for better flow.


it will most likely work fine as long as you have a
cleanout at the bell near by just in case it were ever to stop
up on occasion


wait and see what happens
 
Last edited:

hj

Master Plumber
Messages
33,602
Reaction score
1,041
Points
113
Location
Cave Creek, Arizona
Website
www.terrylove.com
reducer

You have created a lifetime of aggravation for yourself. You NEVER reduce the size of a drain line in the direction of flow. If you could find an eccentric reducer so that the bottom surfaces were level, then it would be less of a problem, but the way you have done it, there will always be a "pond" of water at the reduction. That pond is going to cause the sewage to slow down, and the solids may stay in the "pond" while the water continues on down the drain. Your problems will be the same as if you had a sag in the line.
 

skip

New Member
Messages
3
Reaction score
0
Points
0
sketch added

Thanks to both repliers. I thought I'd add a sketch to help show the connection I made that I'm concerned about. I connected the PVC to a cast iron WYE that is horizontal (pointing slightly down pitch). While I won't have the puddling suggested, I also don't have the benefit of going into a vertical run. This is in a crawl space at ground level as the cast iron is going to the sewer. I did put a 3 inch clean out about 30 feet upstream in the 4 inch PVC. Its in a closet on the main floor. Any more thoughts?
 

Attachments

  • Drain 4 to 3.jpg
    Drain 4 to 3.jpg
    37.9 KB · Views: 1,551

Master Plumber Mark

Sensitivity trainer and plumber of mens souls
Messages
5,533
Reaction score
354
Points
83
Location
indianapolis indiana - land of the free, home of
Website
www.weilhammerplumbing.com
oh , it will probably work....

well it will probably work out ok because you
are on a verticle drop into the wye.... you got lucky there..


its all done now, but a clean out near that spot might be
good...but if you put one back about 30 feet , it just
means you got to get a cable with at least 40 foot on it...


by the time the water gets down the line 20 feet or so
it is going to be running pretty flatin that 4 inch pipe
and will most likely not know the difference when it gets
dropped into the 3 inch...

if you used a 4x3 FERNCO it should slide right through with
very little aggravation
--------------------------------------------------------------------

Of course, this isnt anything I would be particulary proud of,

mistakes do happen, but I would not be bragging
too much about this one

and you might want to hide that mess under a mound of
dirt if you ever plan on sellling the
house someday...or it could very well come back to haunt you..

but all in all it will most likely work for a long time...


just wait and see
 
Last edited:

Finnegan

New Member
Messages
248
Reaction score
2
Points
0
Location
CT
I agree. While this is wrong, it should work ok. I would not bother with adding the clean out until you need it.
 

skip

New Member
Messages
3
Reaction score
0
Points
0
why not 3"?

Oddly enough the house has two different sewer connections. One running to the north that serviced the bathrooms, which was 4" cast iron,and this one I tied into which is the 3" going to the south, servicing the kitchen/laundry. The 4" had tree root problem that would clog up once/year and so I wanted to stop that. Then I was worried I traded one problem for another. I actually didn't realize the one to the south was only 3" until I ran the new 4" PVC over to it (about 30 feet) and then went to tie in. Its in a separate crawl space for the kitchen addition versus the main house.
 
Last edited:
Top
Hey, wait a minute.

This is awkward, but...

It looks like you're using an ad blocker. We get it, but (1) terrylove.com can't live without ads, and (2) ad blockers can cause issues with videos and comments. If you'd like to support the site, please allow ads.

If any particular ad is your REASON for blocking ads, please let us know. We might be able to do something about it. Thanks.
I've Disabled AdBlock    No Thanks