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Question DetailsAsked on 9/18/2014

Water from only the kitchen sink over flows from basement drain.

House built in 1942. Only water from the ktchen sink is over flowing from the basement drain.
The kitchen and main lines have been professionally roto-rooted, high pressure water run through the main line (not the kitchen line) and a camera through all the lines including down the roof vent. All lines were clear. What could be causing the overflow? Would putting in a backwater over flow resolve the issue or is that effective only stopping water backing up from the main sewer line? The roto-rooter man said to plug up the drain but I am reluctant to do this as this is the only drain in he basement. What could be causing the over flow only when the kitchen sink is drained and nothing was seen in the camera and all lines were roto-rootered? What do you suggest can be done to stop the kitchen sink over flow from basement drain? Backwater over flow, replace basement floor drain? Please advise...I'm desperate. Thanks!

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2 Answers


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This is very common with water from the washing machine, as it dumps water out at the highest flow rate of any source in the house, so when the sewer main pipe is getting partially clogged up or reduced in diameter due to grease and soap scum and algae/bacterial buildup, washing machine water is commonly the first to back up, followed by toilet flushing, then tub emptying, then sink emptying - but if you are sure it is the sink and not washing machine water doing this, that might not be the cause.

Backflow preventer would not help I don't think, and with a floor drain you do not have enough head to open a backflow preventer, so the floor drain would not drain when needed. They do make floor drain fittings with backflow preventers - I just have never seen one I would trust to stop backflow (especially as floor drains crud up pretty fast) and still allow water fro the floor to drain down the drain, because there is only an inch or so of head on the preventer when the floor drain is full of water - not the several feet usually available to open the backflow preventer valve.

Were ALL lines roto rooted - INCLUDING the floor drain trap ? I bet not. Sounds to me like you have something called an Everwet Floor Drain (or similar), from American Ductile Iron Company if my foggy old brain runs true, which was pretty popular at least on the west coast into the 60's or maybe even 70's. It was designed so a low-flow-rate gray-water source like the closest sink, and commonly the kitchen sink because that was the only low-flow (not clothes washer) strictly gray-water line in the sewer system, ran into a floor drain through a side-inlet in the floor drain ABOVE the trap, that looks something like this image (could not find an actual picture) but with the kitchen line coming into it from the right side of the image through an additional port, at about the level of the black plug but on the right side in the image -

The intent was for the graywater (kitchen sink drainage) to refill the trap in the floor drain with fresh water every time it flows, then flow out through the trap (to the left in the image) to the main sewer line. That way the floor trap never went dry and let sewer gases in - similar to the trickle systems used to keep laundry room or hot tub overflow floor drains full of water.

If the floor drain trap plugs up (as it can easily do especially if you have a garbage disposal, which this type of trap was not designed to take debris from), it overflows ONLY when that particular incoming source is used - like your case. The solution is cleaning out the floor drain trap. Usually (not guaranteed), as long as some water will go through it, you can do this by just pouring a few gallons of full-hot water with some liquid dishwashing soap in it down the floor drain as fast as it will accept it. If more clogged up AND if it drains at least partly, then try foaming drain cleaner or a plunger - usually takes a cone-shaped type plunger to get a good seal. If that does not do it then it is probably full of inorganic grit - you can flush it by taking a garden hose wrapped with a rag and shoving that (using the rag as a pass-through gasket in the top of the trap) in the top of the floor drain, then having a second person hit it with a few short shots of water will flush it out. Short shots in case it backs up on you (drape a towel around the hose/drain area so any overpressure spray escaping around the gasket will not hit everything in the room), and also to let it drain back down so you don't overflow the sewer pipe up to the next higher drain opening, like probably the kitchen sink. In the most severe cases you have to snake it, or use the hose with jet spray nozzle and without rag in short shots in the drain to flush the debris out while you wet-vac up the water, or intermittently fill with water while sucking it dry with wet vac using a rag same way to provide a seal to get a suction on it to get out the debris.

Note for hose or suction, the rag plug should be BELOW the incoming kitchen line if at all possible, so all the action is through the trap. Remember when you are doing these things, it is the TRAP you need to clean, not the bypass passage (which might or might not exist in your particular floor drain) with the plug,, although vlushing that first is probbly a good idea, and would quickly tell you if the blockage is in the trap, or downstream of the trap fitting. If water doesnot flow freely through the bypass when the plug is out (assuming you have one), then the blockage is definitely downstream in the sewer line from the kitchen and floor drain, and the roto-rooter guy failed in his mission. That plugged passage is designed to allow snaking or rooting the downstream sewer line from that point on, which is why it is normally plugged - otherwise sewer gases could come up through there.

If you have a trap with the bhypass, sometimes they are quite tight, so pouring water down while snaking, or making up a hose fitting on a small-diameter hose barb and flexible rubber hose is needed to get it to snake down into the trap, if just blasting it out with the hose does not work.

This problem is surprisingly common in quite old houses from the post-war era, particularly in houses where the connection is at the garage floor drain where a lot of sand and grit off the cars goes down the drain and eventually plugs it solid.

Once you get it fixed, short-term solution is flushing the trap with a hose every year or more often to clean it out. Long-term fix is to replumb that line so it goes straight to the sewer line, not to the floor drain trap - easiest way probbly to remove the floor drain and a short length of sewer riser to it, put in a side wye for the kitchen drain, then reinstall (or probably put new plastic one) floor drain into the wye.

Only other thing I can think of that could cause this if you do not have the Everwet type of drain, since you said the camera went down the kitchen line fine, is a crack in both the kitchen line near the floor drain AND in the floor drain casting (probably where they come together in a wye) that allows the kitchen drainage to come up into the floor drain - but that would mean that is an easier path than going through the sewer pipe, which should not be the case if it was routed out.

Unfortunately, your drain cleaner blew it and missed the whole point - if the kitchen drain line was the problem, the high-pressure cleaning should have gone down through that line first (after putting an expanding rubber plug in the floor drain to prevent it from coming out there) to be sure it was thoroughly cleaned out - because if it is gunked up with grease between the floor drain and its junction with the other sewer pipes in the house (from bathrooms) before they lead out to the street, then he did not solve the problem, though the camera should have shown at least a partial blockage or full-diameter decrease due to grease buildup or sediment in the line. That is a very common place for a blockage, because if not plumbed right, and especially if they come together close together, solids and paper from the toilets come down in to the main sewer pipe, and if it has not been routed out recently it is easier for it to backflow into the other pipe leading from the kitchen, and it sediments that pipe in, eventually blocking it in the horizontal run, especially if horizontal into the joining wye instead of coming in significantly higher in elevation than the toilet line(s).

Answered 6 years ago by LCD


One afterthought, in looking at this question as a possible reference for answering a similar question:

IF you don't know for certain that that particular line that the floor drain is on was routed out, it is possible you have a separated graywater system - washing machine, sometimes sink and dishwasher, showers, sometimes sinks - which goes somewhere other than the sewer line to a septic tank. Done to reduce the water infiltration load on leach fields in low-infiltration (clayey oir silty) soils. IF that were the case, perhaps the kitchen sink is the only source connected to that floor drain.

Another possibility that came to mind - that the floor drain is on a branch drain line coming direct from the kitchen sink AND is partly blocked between the floor drain and where that stub line connects into the main sewer line, which itself is NOT blocked. So, that floor drain overflows when kitchen sink water comes down the stub or branch drain line, but all the other sources go on the main stack and have no reason to back up into that branch line.

Another thing that happens if that is the case, especially if the washing machine is not on that branch, is that because it is a low-flow line (especially if sink is never filled full with water due to having dishwasher, eatc) is that solids from the main stack get diverted into the branch, gradually sedimenting it partly full, thereby partly blocking it, because the branch does not have a high-flow source (washer, toilet) capable of flushing it out periodically. This also promotes backwatering of the sink/dishwasher flow and its contained grease, so it blocks off with food debris and grease faster than if another large water source were running through the branch also.

Either way, if prior responses did not lead to a suitable solution, running a snake or jetting tool down the KITCHEN drain into the main sewer stack should clear it out. OR routing out with full diameter scraper head to clear the grease accumulation and restore the line to full diameter, which should generally be done every 20 or so years anyway to clear accumulated grease and fiber buildup.

Answered 5 years ago by LCD

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