Plumbing for Suds Pressure Zones
By Fred Bretzke
I remember when I was a young newlywed. We were renting a 60-year-old bungalow in southwest Calgary shortly after I had received my journeyman ticket and Red Seal. It was in February, just around Valentine’s Day, and I knew I had to remember two things: make sure all the mechanicals in the house were working and buy a Valentine’s gift.
There were two significant problems my wife began to complain about after we moved in. Our clothes didn’t seem as bright and clean as they should be, and she also thought the dishwasher was broken, because we always ended up with stained dishes. (Maybe that was because I always bought the cheap detergent.)
I did what any good husband would do: I agreed with her, but didn’t do much else. At some point I finally broke down and bought the most expensive laundry and dishwashing soap I could find, just to appease her. But as time went on, our clothes and dishes were still dirty, even with the expensive soap. Now this was starting to bug me, so I commenced my plumbing investigation.
Sussing Out the Suds
As a plumbing P.I., my first step when I decided to get to the root of our appliance problems was to take a look at the basement laundry in more detail.
I knew the laundry tailpiece was just lying on the floor draining into the floor drain. It made a pile of soap suds around the neck of the floor drain, but so what? They were only suds, I thought.
I put the new washing machine through a few cycles just to see if it was working properly. As it went through the rinse cycle it did seem to push out some suds and the water wasn’t that dirty.
I then went to the dishwasher and ran it through a few cycles. The glasses were still stained. As I looked under the sink, I noticed that the dishwasher’s 3/4" black rubber hose was not installed into the continuous waste under the sink. The drain hose disappeared into the cabinet floor and then ran into the basement.
In the basement, I took a few ceiling tiles out to expose the ceiling. Lo and behold, I discovered the hose pipe hooked into a P-trap below the floor, which was then piped into the stack in the basement.
There were no leaks or backups, but I did remember that every time I installed a dishwasher I had to install the drain hose as high as possible under the counter and hook it into the continuous waste upstream of the kitchen P-trap.
Saving the Day
To complete my story, I decided to reinstall the hose correctly above the floor and tie it into the food disposer, which was installed upstream of the kitchen P-trap. After that, I ran the dishwasher through a cycle full of dirty glasses and—voila!—out they came shiny and crystal clear.
My wife would be so happy. Maybe I wouldn’t have to buy her a Valentine’s gift after all!
I learned that the reason we install dishwasher hoses as high as possible is to prevent the dishwasher from gravity draining. Otherwise there won’t be enough water volume during the rinse cycle, hence, dirty or stained glasses.
By now I was in Superman detective mode, so I figured I might as well get in my wife’s good books and fix the washing machine problem too. I might not even have to get her a birthday gift, let alone something for Valentine’s Day!
I returned to the scene of the crime, where a brand-new washing machine sat defiantly in the dark concrete corner right in front of a suds-spewing floor drain. I figured if the code said that a dishwasher’s hose must be installed as high as possible, it must be the same for a washing machine.
So I broke out the floor and installed a wye in the branch. I ran a new 2" ABS drain over and put a stand pipe complete with P-trap up the wall 36" high. This would accommodate our new washing machine’s wash cycle, keeping the water volume nice and full, and letting the pump push the water up the hooked drain hose and down the 2" standpipe.
Sure enough, it worked. Clean dishes, clean clothes, and I even bought my wife a Valentine’s gift with all the money I saved buying cheaper soap!
National Plumbing Code:
Where a domestic dishwashing machine equipped with a drainage pump discharges through a direct connection into the fixture outlet pipe of an adjacent kitchen sink or disposal unit, the pump discharge line shall rise as high as possible to just under the counter and connect:
a) on the inlet side of the sink trap by means of a Y fitting, or
b) to the disposal unit.
Suds Zones in Buildings
In a commercial building, we would typically multi-storey wet-vent washing machines as they are only two-fixture units, and you are allowed to wet vent up to four-fixture units per storey above the first storey, as per the 2015 National Plumbing Code.
But this would become a problem as new washing machine pumps would discharge soap suds 40 times the diameter of the wet vent, up and down the pipe. This meant that if you installed a 3" wet vent, the soap suds would travel up and down the wet-vented stack for 10 feet after leaving the washing machine.
If any other plumbing appliances were installed in that suds zone area, they would leave suds backing up through sink drains.
This would not only present a cosmetic issue, but the suds would eventually solidify and plug all the vents.
The 2010 Canadian National Plumbing code included a new table—18.104.22.168. Maximum Permitted Load from Fixtures with a Semi-continuous Flow—to size the fixture unit load and P-traps for commercial washing machine drains based on their litres-per-second pumping output. This meant larger pipes would be installed for high-output pumps.
Other recommendations were made in the appendix of the code (A-22.214.171.124.(4) Suds Pressure Zones). This advises that high-sudsing detergents used in clothes washers produce suds that tend to disrupt the venting action of plumbing systems and spread throughout lower drains.
One solution is to create a suds zones stack separate and downstream from all other stacks. This serves to keep the washing machine multi-storey wet-vented stack separate from all other fixtures and stacks.
It’s also advisable to keep all fittings, such as wyes and 45s, as streamlined as possible, increase your building drain one size larger than normal and, finally, install check valves on all the washing machine fixture outlet pipes that are tied into that suds zones stack.