When my washing machine is draining every once and there is some water overflow. It's not a huge amount, but any amount of water overflowing is unexceptable.

I was reading a previous thread where people were discussing this and it generally involved septic systems.
We are on a municipal sewage system.
We bought split level house a little over a year and a half ago and the 2 lower floors, one at ground level and one basement to do.

On the ground level was a washroom/laundry room that needed to be done. The washer and dryer were in this room as was a fitting and drain for a toilet to and s drain for a sink.

We decided to take the washer/dryer out of this room and install a sink on the exising washing machine drain. We broke open the floor and ran a drain for a stand up shower in place where the original sink drain was installed. (I hope that was clear if not let me know)

We moved the washing machine into the back room. We installed a p-trap where washing machine used to drain, then we had run the drain pipe into the back room.
The pipe runs parallel to the floor (approximately a foot off the floor) on a slight downward slope from the machine. From the trap it goes about 1 foot, 90° angle and then about 8 feet to the back room, 90° angle to go up. The "vertical stand" I believe is what it is called is about 30".

Could it be the vertical stand is not high enough or could it be the slope is too level?
I'm positive there is no blockage.
This started as soon as we moved the washing machine.

Thanks.
If a drawning is needed let me know.

You left out the few details that would be helpful. Slope must be stated more clearly, code requires 1/4" per foot for drain lines smaller than 4" What is the size of the new drain line your ran, 2009 codes calls for 3" since the old 2" pipes clogged too often.

Hmmm then that's likely where I went wrong.

The slope I believe was about 1/4" per ft but I the original drain was 1 1/2" and so we continued 1 1/2". Also the sloped section is about 7 feet long. I presume now that this section likely doesn't empty fast enough.

After doing a little research in the rest of the house I believe under the floor the piping size was being increased to 2" and we probably should have put the entire drain at 2".

The drain from our kitchen comes down into an unfinished basement (walls are still open making it easy to see) it's 1 1/2" straight down into the basement and as it goes under the concrete floor it is sized to 2". I believe this is how the original washer drain must have been on the ground floor.


Related question regarding the kitchen drain.
Above I mentioned how the kitchen sink drains through 1 1/2" into an unfinished basement and goes into a 2" pipe into the floor.
Could I put a Y on that 1 1/2" and have a washer drain into it or would it be better to increase the size to 2". Figuring it's a straight downward drain and the section that is 1 1/2" would only be about 3ft?

Also you mentioned that new code is for 3". I assume as long as 2" is under the concrete I can't increase size to 3"?

Thank you for your reply.

Samsara, part of your issue is the old code required at least a 2" drain line for the washer all the way, or larger. 2009 code will require a 3" pipe since there are too many issues happening with 2" drains and the newer machines.