Splicing into existing 3" PVC sewer line

I have a 3" PVC sewer line connecting to toilets, showers, etc. There is also a seperate 2" sewer line that handles the kitchen sink (with garbage disposer) and d/w. The two sewer lines currently exit on oppisite sides of the building.The separate sink line exists because there probably was a seperate drainage pit for the sink prior to sewers being installed 25 years ago. Because the 2" pipe from the kitchen sink to the main sewer is a long one, it gets clogged. I'd like to re-direct the 2 inch pipe from the kitchen (in the crawlspace ) and connect it directly into the 3" sewer line (a much closer, direct path).

Question: I will have to cut into a section of the 3" sewer pipe run, and insert the appropriate fitting to connect to the 2" pipe. How best to do this? Is there a PVC slip joint fitting for 3" pipes? Or, is a no-hub clamp connector an option for splicing into the 3" line?

Niles said:

Question: I will have to cut into a section of the 3" sewer pipe run, and insert the appropriate fitting to connect to the 2" pipe. How best to do this?

Click to expand...

A few months ago, I used what is called a saddle to do what you are describing. In my case, I was adding a 2" discharge from a sewage sump to the existing 4" line going out to my septic tank.

A saddle is just like it sounds: a PVC fitting that covers about half the diameter of the existing pipe and has a hub (like a saddle horn, but in the center) for the second pipe. I installed mine by gluing it in place and attaching the accompanying u-bolts for good measure, then using a hole saw down through the hub to cut a right-sized and properly-located hole in the existing pipe.

Niles. From what you say, the kitchen sink used to drain in one direction and now it drains in another. You haven't mentioned if this line has any drop (or fall) to it. Put a level on it. It should drop 1" to 2" every 4 ft. It also should have support or hangers every 4 ft. The saddle tee is something I've never used. In a another thread I just described a "repair coupling"... I've also used no hub couplings. I found the repair coupling to be easier to work with. It doesn't have a stop in the middle like regular couplings do. Therefore, you can slide it up the pipe and out of the way, insert your tee with short pieces of pipe (or nipples) cut to fit and glued in the fitting, then glue the repair couplings in place when you slide it over the connection, seam, or whatever you call it where the ends of two pipes meet. I found the repair couplings at HD but not at Lowe's... if you ask, you might find them or have them ordered in for you. Big plumbing supply houses should have them.

Thanks RandyJ and leejosepho.

I DO have a saddle T (which I could only find at Menrds, not Lowes or HD). At first, I thought this was the answer, but then I thought, maybe not. My concern is that a saddle T (or any kind of straight T fitting) may be susceptible to clogs from garbage disposer debris. I concluded that the best kind of connection would be a "wye" type connection (3" x 3" x 2") [with a sloped entryway for the 2" line, instead of a straight right-angle entryway for the 2" line.]

So, the "repair coupling" might be the answer to enabling the splicing in of a wye connection.

Any comments on my concern about a T connection vs, a wye connection for the garbage disposer line?

The drop for the 2" line is a concern, and I will have to see if I can achieve the drop while still connecting into the 3" soil pipe. The 2" line goes out (underground) and presumably has its own drop (underground) while wending its way to the main sewer line. But, the drop (or lack of it) may be another reason for its tendency to clog. I do not know how professionally the house was connected into the sewer system years ago. Because the crawl space is literally a space that allows you to barely crawl, my guess is that the contractor at that time may have decided it was simpler to install a 60 foot pipe from the existing kitchen septic tank to the sewer main outside, rather than connect into the closer main beneath the house. So, maybe neither solution will have a perfect 1" per 4' drop.

How significant will this issue be if I cannot achieve a good slope on the disposer line? Are there any statistics that say, for example: You will probably get a clog twice a year if you don't have at least a 1' drop per 4 ft?

If that saddle T is on its back facing up it is wrong it needs to be a Y and saddle Ts are not ever allowed to be used here at all.

If you cut apart a pvc drain line you usually can get enough spring for a wye to fit in. If you can't get the spring, you can use no-hub couplings instead of slip couplings. I really don't like slip couplings.

Pretty much the reason for the 1% to 2% slope is so that the water floats out the waste. If it is too steep the water can out run the waste and contribute to a clog. The big reason for a y rather than a 90 is so that you can get a snake down it easier to clean out if needed. I'm sure it is also to keep the solids flowing rather than slamming into a corner and getting stuck there. Of course, the smoother the inside of the pipe and the fewest ridges of any kind...the better and less for "stuff" to get hung on.

Niles said:

Any comments on my concern about a T connection vs, a wye connection for the garbage disposer line?

Click to expand...

Not being a real plumber, I know little about codes. Being an accomplished fabricator, however, I use some practical logic and consider the *reasons* for certain codes I might know when deciding certain applications in my own stuff. For example, I would not have used that saddle in my picture to dump a toilet straight down into the main line, but the slurry discharged from a sewage pump is not as likely to "pile up" ... and on top of that, the hub you see just ahead of that saddle is the hub of a 4X4X3 long-sweep 90 with a cleanout on the end and receiving the discharge from a toilet about 12 feet above it. And since the second-floor toilet gets flushed far more often than the basement sewage pump discharges, I cannot imagine ever having to open that cleanout.

So then, and unless "the letter of the law" is your biggest concern, I would look at the flows and drops of each line and at how much room and flexibility and so on you have while trying to imagine a worst-case scenario to see how likely you are to have a problem. And of course, always consider the hard-won experience and advice of the experts right along with all of that!

"Pretty much the reason for the 1% to 2% slope is so that the water floats out the waste. If it is too steep the water can out run the waste and contribute to a clog. The big reason for a y rather than a 90 is so that you can get a snake down it easier to clean out if needed. I'm sure it is also to keep the solids flowing rather than slamming into a corner and getting stuck there. Of course, the smoother the inside of the pipe and the fewest ridges of any kind...the better and less for "stuff" to get hung on."

randyj,
that's wrong. Water doesn't outrun waste. There have been university studies on this. I have seen many long runs at steep angles, and they don't clog up. The code calls for minimum pitch, not max.