Yeah, I'm a crappy plumber. 
Did some work for a friend, the original setup emptied into a leach field. For various reasons it's necessary to tie the drain into the house plumbing which now goes to city sewer.
The drain stuff above floor level in the laundry room was redone a couple years ago with 1 1/2" PVC pipe and tied into the original galvanized 1 1/2" stuff and it has a roof vent. It dropped straight down about 3 feet, then turned 90 degrees and went out maybe 20 feet from the house before it went to the old leach field clay pipe. The following problem did not happen with the original setup.
I cut all that away, came straight down maybe a foot with 1 1/2" PVC, turned the new pipe 45 degrees with an elbow, went down another ~2 feet and into another 45 which now goes into a 1 1/2" diameter PVC pipe for about 12 feet. That is connected to a 2" galvanized pipe which comes straight down from the kitchen sink, that drain system has its own air vent through the roof as it should. The connection is at a tee, my pipe enters at one side of the tee. If you think of it as an upside down capital T, it comes in on one end of the cross and the stem of the T points up toward the sink. My pipe is angled down at about 10 degrees, the pipe it goes into is angled down about 2 or 3 degrees. That means my entire run angles downward, there's no high or low spots to create a half assed P trap.
Now what happens: when the washing machine drains into the 'stack' pipe, it runs through the original P trap just fine but my new stuff backs up. I can see this because there's a cleanout in the air vent maybe 2" above the P trap, if I take this out and watch the water flow it comes quickly out of the P into the new stuff but that pipe will rapidly fill above the level of the P trap and that means the machine drain overflows. Cut off the machine, the new pipe drains almost instantly. Yeah, weird.
The machine drain is normal 3/4" or so hose, I can't find anything clogged. My first thought is to replace the 1 1/2" with 2" but I don't think this addresses the real problem. Any of you smart guys out there got any ideas?
Not a plumber, nor very knowledgeable. But-
Washer in the house I live in backed up to the extent of flooding & overtime had overflowed behind the sheetrock & caused some significant water damage to floor joists. When we finally got someone here who knew what to look for (3rd or 4th attempt), he discovered that the washer drain had been jacklegged with 2 90 degree connections close to the higher end of the drain pipe & less than a foot apart. This arrangement wouldn't drain fast enuff to drain the washer. We had to move the washer a few feet & plumb the drain directly vertically to the waste pipe. The 2 45 degree elbows may be your problem. At least you're aware of this & hopefully have caught it in time to not rot floor joists, sub flooring etc.
I'm not a plumber either, and I didn't stay in a Holiday Inn Express last night either, but I agree. The two 45* fittings are probably slowing the flow down just enough to back it up.
Hmm. Interesting. The original setup dropped maybe 3 feet into a single 90, but it did drop straight down. I used 2 45's and avoided 90's because of what y'all mention. Wonder if I should go for a straight drop and larger diameter pipe with a 90 at the bottom of the drop like the original setup?
The old straight drop was letting the water gain more velocity before it hit the bend?
Well, got back into it today. Went from 1 1/2" to 2" pipe, created a straight drop with a long elbow which goes into the original 2" galvanized stuff and therein hangs a tale.
The 2" galvanized stuff has ~40 years of mung and goo in it making the effective diameter ~1". I cleaned out as much as I could as far as I could (nasty job) but there's approximately 15 feet of pipe which is gooped up which then turns 45 degrees and disappears under a slab in the general direction of the downstairs bathroom. Nope, uh uh, not messing with that. Time for her to call in the big guns. 
Where the tube leaves the washer, is there a vent device?
914Driver wrote:
Where the tube leaves the washer, is there a vent device?
+1, how does the air get out? You should have a vent on that somewhere.
Mine had the same symptoms, went through three different vents before I found one that worked.
As far as vents, there's two on the line: one at the 'drop' for the washing machine drain, then another at the 'drop' for the sink. That one also incorporates the diswasher drain. The two vents are about 15 feet apart.
What happens: when the washing machine finishes its cycle and drains, the water goes through a 1 1/2" pipe approx 24" tall into a P trap, the P trap connects to a vertical 1 1/2" pipe with a vent at the top. The stuff inthe wall looks like this:
only there is a 'cleanout' just above where the P trap connects. I took the cap off the cleanout to make sure the roof vent wasn't clogged with pine straw, dead squirrels etc, ran the washing machine and no joy.
This stuff goes into a straight drop which goes into a 2" pipe (my new stuff) which then goes through 2 45 degree elbows approx 15" apart (necessary to get the pipe away from a concrete block foundation wall) then drops another 10" into a 'long' 90 degree elbow, then through a ~ 10 foot long 2" PVC pipe angled downwards about 5 degrees. At the end of this is where it connects to the existing 2" galvanized which seems to be the source of the problem. If it's not connected, the new stuff drains like crazy. If it's connected, the vertical 'drop' will fill with drain water, if the flow to it is shut off it drains quickly but obviously not quickly enough.
The existing 2" galvanized is goopy as noted, it angles down at about 2 degrees or so over a 15' run and goes into a galvanized 2" elbow which disappears into the dirt.
EDIT: I thought about adding another vent, what concerns me is that the position of the pipe means I'd have to run it a loooong ways before it could be teed into an existing vent or run it up through a wall. An air gap type setup is an option but not a good one because if it were to leak it would create one hell of a mess under the house.
OBTW: the original stuff also had 2 45's in it for the same reason I put them there, i.e. to get past the foundation wall.
I'm at the point where I think what's happening is the water from the washing machine is hitting fast enough that the drain pipe temporarily gets pressurized due to the goop in the 2" galvanized. The second vent is of course above the P trap for the sink, that means the water in that trap acts as a seal. Hopefully snaking that out will fix the problem, if not I'll have to add a second vent to allow this pressurized air to escape. I do know this is an aggravating sumbich of a problem.
<----not a plumber, but sounds like an air bubble.
I don't know the plumbers term, or whether it's to code, but mine has sort of bypass.
Basically, drain hose from washer, rests in the drain pipe, open vented to the air.
It has a t, off of it, that reconnects to the drain with another T.
In reply to sachilles:
Yep, that's what I'm thinking will have to happen.
I'm thinking so long long as you have a trap in the "vent" portion it should prevent any gas from entering the house, yet allow it to burp.
Well, it's fixed. All my stuff was done right; it turns out the big drain under the slab was clogged with 40 years of goo. $89 worth of pro snaking later the thing drains so fast it sucks small children in.
yamaha
UberDork
7/16/13 12:25 p.m.
In reply to Curmudgeon:
Oh no, which of the little curmudgeons were lost?
Call me if you have to toss it and get a new one 
