Utility Sink Standpipe Conversion

My washing machine just overflowed the utility sink for the last time! I want to tear out the sink and have a 2" standpipe instead. The sink drain/trap is 1.5", goes into the wall with a cleanout right underneath it and a vent stack right above it. The house is built on a slab and all drains are cast iron (the vents all appear to be galvanized though). The cleanout looks like 2" but it's hard for me to tell for sure (do they make 1.5" cleanouts?).

Before I start tearing out drywall, can anyone tell me at what point the 1.5" usually transfers to 2"? I am not sure how to proceed. The new standpipe/trap will all be 2" ABS and connected by a Fernco coupling, but just not sure where it will connect so there's not a bottleneck.

Thanks

You must make sure the entire drain line is 2" or more. You can't put a 2" standpipe into a 1-1/2" drain. The rule is never reduce the size of a drain. You mentioned using a Fernco coupler. Fernco is a brand name that we often use incorrectly to refer to a neoprene sleeve with 2 hose clamps. This type of connector is illegal above ground. If you must use a clamping type connector, get the no-hub kind. These have a single clamp over the entire sleeve and will provide a much more ridged connection.

I appreciate the feedback. I will use a shielded no-hub connector for sure, no worries there. And I understand about not creating a bottleneck, which is why I am asking where the 2" usually begins after a 1.5" drain -- I want to eliminate all the 1.5" and tie-in a 2" ABS standpipe/trap into the existing cast iron. I want to do this right so I never have to do it again!

The 2in. usually comes thru the concrete and them changes sizes, most areas don't allow anything smaller underground.

Thanks, that's what I figured. I suppose I'll have to cut the cast iron just above the plate, remove the vent stack along with the p-trap, then replace it all with ABS. I guess a no-hub coupling is OK with a vertical stack of ABS that will be about 12 feet tall?

overfflow

WHY did the sink overflow? Usually the reason for using a sink is because a standpipe drain might overflow. IF a standpipe is really better, and you do not just have a plugged drain, (which a standpipe would not cure), then you need a proper sized connection for it to go into the drain line.

If you get a front loading washing machine, it will use much less water, and a whole lot less soap so you get far far less sudsing too. Then, the problem you now have may disappear completely. This doesn't increase your flow, but it stops the overflowing. A small front loading washing machine holds a lot -- it's surprising, compared to top loading ones. All front loading washing machines clean better than top loading ones.

The sink has overflowed on several occasions. A couple times it was because the cast-iron pipes had become clogged with acrylic yarn and hair; I've since put lint filters on the lines and had no more problems with clogs.

More often, it's because the drain opening has become accidentally blocked by a bit of laundry. I got one of these this week (http://www.innovationsexpress.com/Drain_Defender.php) and I have high hopes that it will stop future clogs from happening. But we're having our wood floors replaced and I want to eliminate all possibilities. Plus, that utility sink is an eyesore and takes up a bunch of precious room in our kitchen. We hardly use it as a sink anyways.