Good Morning Jeremy,

I received your drawing via email and have reviewed it thoroughly.

Before we begin, let me take a moment to commend you on both your code research and the proper use of fitting nomenclature. This is the type of description I would expect to receive from a 2nd year Apprentice; you have done your homework well.

You are correct in your assessment that the original installers made this project far too complex. Not only can you combine the lavatory and shower or tub drains as you suggest as we go deeper into your project you will see that there is a distinct advantage in doing it in that manner.

If I am understanding your description correctly on your main CI stack you have a 4" CI Double Tee (Sanitary cross) with a 4" closet bend to the closet flange on either side of the stack, then directly above that you have a second 4x4x2x1-1/2 Double Tee for the shower, tub and lavatory drains. We can simplify this but I would be hesitant to remove any fitting from that 4" vertical stack because cutting into a CI stack can be a very dangerous undertaking. CI stacks are extremely heavy and in most cases they were originally installed to be self-supporting or at best a couple strap-hangers that have by now rusted through or perhaps a couple pieces of wood blocking, which was crudely fastened in place. If you cut a section out you have the risk of the remaining stack above the cut falling down, causing serious structural damage as it rips waste arms out of the walls, possibly ripping a large opening in your roof and not to mention the risk that it would fall on you, causing serious personal injury or even death.

I would begin at the 4" sani-cross where the closet bends are attached. Using a CI snap cutter cut the CI about 3" from the face of the hub leaving enough so that you can attach a rubber 4x3 reducing Fernco coupling

NOTE: when your house was built the WCs had a 3.5 or 5gpm flush rate and required a 4" drain. When 1.6gpf WCÂs were first introduced they had serious problems with clogging. It was later determined that a 1.6gpf WC should be on a 3" line to reduce clogging.
From the 4x3 Fernco you can connect an ABS "3x3x2 side inlet closet bend to a 3" closet flange, then run a 2" line to both the tub and the shower. The reason for enlarging the tub drain will be apparent in a moment. (Note: Code standard for a tub drain is 1-1/2" however there is an exception in the code which allows us to increase the size of a trap or drain line by one nominal trade size of pipe.)

Next install an 1-1/2" riser in the wall behind the lavatory, with an 1-1/2" Tee for the lavatory waste arm to the lavatory trap and connecting the top of the riser to the existing steel vent with an 1-1/2" Fernco rubber coupling in the manner that you described. At the base of the riser you can install an 1-1/2" 1/4bend, however, given that the connection will be in the stud bay in the basement, and in an accessible location, I would prefer to install an 1-1/2" Wye & 1/8bend or a Combo, with the side opening connected to the riser. On the upstream end of the Wye or Combo I would then install an 1-1/2" female thread adapter and an 1-1/2" screw in plug to form a cleanout for the horizontal drain line.

For each lavatory drain I would then run a 1-1/2 line straight from the base of the riser to the point where it will intersect with the tub or shower drain line at a right angle. Connect the lavatory drain to the tub or shower drain line by means of a 2x2x1-1/2 Wye & 1-1/2 1/8 bend or a 2x2x1-1/2 combo. (If you canÂt find a reducing Wye or Reducing Combo you may use a straight 2"Wye & 2" 1/8bend with a 2"x1/2" reducer but be careful here, a Tee would be prohibited.)

In this configuration the tub and shower drains are wet vented from the lavatory drain thus all the tub and shower drain line on the downstream side of the Wye & 1/8bend is defined as a "vented branch" and the remaining short run on the upstream side of that Wye or Combo to the tub or shower trap is well within the 5Â maximum length limit for a 2" waste arm.

The reason that we increased the tub drain line from 1-1/2" to 2" is because under the UPC an 1-1/2" horizontal branch line is limited to 1dfu, which is not sufficient for a tub drain, which is 3dfuÂs, however by increasing to 2" the line is rated for a maximum of 4dfuÂs, which is enough for both the tub(3dfu) and the lavatory (1dfu).

If you have the second sanitary cross on the main stack as was mentioned before you can now cut the lines on the side inlets about 3" from the hubs and cap the lines with rubber Fernco caps.

Note: for cutting the CI I would strongly recommend you rent a "CI snap cutter". Most tool rentals will rent a snap cutter for about $15 a day, and with the snap cutter you can make a good cut in about a minute. CI can be cut with a reciprocating saw but in my experience it will take about 20 minutes per cut and you will burn up so many blades that it will end up costing more than the rental cost of the snap cutter. CI can also be cut by means of a circular saw or side grinder with a metal cutting abrasive wheel, but using an abrasive wheel is never a good idea. Keep in mind that sewer gas is highly flammable and potentially explosive, not to mention the shower of sparks and debris you have from the wheel, and here again, if you figure in the labor time and cost of the cutting wheels it is still more economical to rent a snap cutter.

Thanks very much for your help and the compliment.
Several things that caught my attention, the bath being 3 dfu's vs 2, the dfu rating of 2" pipe is only 4 dfu's, and especially the flange size info on the 1.6gpf WC.
Thanks again.
I have heard a lot of people complain about the early versions of low flow WCs, and it only makes sense they would have been dropped onto an existing 4" line.
I plan on putting in new comfort height 1.6gpf toilets. Is changing the flange enough, or does the bend need to be 3" also?

"If I am understanding your description correctly on your main CI stack you have a 4" CI Double Tee (Sanitary cross) with a 4" closet bend to the closet flange on either side of the stack, then directly above that you have a second 4x4x2x1-1/2 Double Tee for the shower, tub and lavatory drains."

The two, 4x4x2x1-1/2 Double Tees, (one for each bathroom) are between the 4" closet bends, and WC flanges on each side. The top of closet bends are about 6.5" below the subfloor.

(I tried to do an graphical drawing here, but the board takes out spaces automatically, which makes it unreadable.)

I have cut the lead Double Tee out of the master bath's CI closet bend hub. Which was no small feat. Stuffed a bag through the Tee into the Closet Bend, and used a recip saw to cut most of the lead off, then through the brass ring, then pried it loose, cleaned out the lead and oakum. This gets rid of all the old lead piping for this bath.

Do the rubber rings (doughnuts) work as well as the no-hubs, to drop a 3" piece of abs into the CI hub of the bend, then use a 3x3x2 Tee. The doughnuts don't look very secure at first glance. I haven't tried fitting it in the hub yet though.

I like the idea of the wye to a clean out under the lavs.
What about under the bath?
An ounce of prevention...