Geniescience
Homeowner
Now I've found the Table, but I cannot see anywhere anything saying that the tailpiece remains at 1.5" until it hits the vented DWV pipe...
DFU load when 2 dishwashers. ( = 3" pipe ? )
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Which table are you looking at? On the Table 7-5 that I found, there is a note saying that it excludes trap arms.
In general, the trap arm is always the same size of the trap. There may be some exceptions to this, but this is pretty muc always the case as far as I know.
In general, the trap arm is always the same size of the trap. There may be some exceptions to this, but this is pretty muc always the case as far as I know.
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MACPLUMB
In the Trades
I think to be on the safe side you need at least 6" or maybe 8" pipe to be sure to drain right !
That will work..we just need thicker walls. 
BTW: I also noticed that 7-3 says "Min. Size Trap and Trap Arm", so that should clear it up for you. You'll probably need 2" in the wall regardless with the 2 DWs. The question is how you will connect the DWs to determine how to size the trap(s).
BTW: I also noticed that 7-3 says "Min. Size Trap and Trap Arm", so that should clear it up for you. You'll probably need 2" in the wall regardless with the 2 DWs. The question is how you will connect the DWs to determine how to size the trap(s).
Geniescience
Homeowner
It's disallowed to size beyond the self scouring ability of a P trap or pipe.
Geniescience
Homeowner
2 DW = 1 DW in practical terms. One collects dirty dishes, while they other is clean and being emptied. They are used as alternate holding places.
It's extremely rare to turn both on, at the same time. Even then, they won't drain at the same time since they have sensors that continue rinsing until "turbidity" levels are clean.
It's extremely rare to turn both on, at the same time. Even then, they won't drain at the same time since they have sensors that continue rinsing until "turbidity" levels are clean.
Geniescience
Homeowner
Clear and concise. I like it that way.
The OTHER plumber on a gardening and homeowners' site lords it over everyone, but it is obvious to me now that he has a lot of ignorance mixed in with his "knowledge". He never posts in any forum where there are other plumbers. He may be an open-book 3-hour-exam kind of Master Plumber. He wrote his exam in Ohio.
In another recent thread about a related subject, it was pointed out that a 1.5" diameter drain pipe is deemed sufficient in Canada for any US made washing machine and laundry tub. When a homeowner asked about putting his washer outlet into the laundry tub, nobody was willing to give him any options. After all, he could move his house to Canada. It is a possibility.
The OTHER plumber on a gardening and homeowners' site lords it over everyone, but it is obvious to me now that he has a lot of ignorance mixed in with his "knowledge". He never posts in any forum where there are other plumbers. He may be an open-book 3-hour-exam kind of Master Plumber. He wrote his exam in Ohio.
In another recent thread about a related subject, it was pointed out that a 1.5" diameter drain pipe is deemed sufficient in Canada for any US made washing machine and laundry tub. When a homeowner asked about putting his washer outlet into the laundry tub, nobody was willing to give him any options. After all, he could move his house to Canada. It is a possibility.
A kitchen sink is plumbed with 2" up to the vent. Then you can use a 1.5" trap arm.
This isn't rocket science. We can paste the code reference, but the question has been answered.
All dishwashers use a 1/2" line, which then dumps into a 1.5" trap and trap arm, and then finally finds it's way to the 2" waste.
Old code used to allow 1.5" for the kitchen waste. Like the 60's was the last time I saw that.
This isn't rocket science. We can paste the code reference, but the question has been answered.
All dishwashers use a 1/2" line, which then dumps into a 1.5" trap and trap arm, and then finally finds it's way to the 2" waste.
Old code used to allow 1.5" for the kitchen waste. Like the 60's was the last time I saw that.
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