Stand Alone Dishwasher Drain

[cds0020]

I am in the middle of a kitchen renovation and have run into a potential issue with how the dishwasher drain was piped in the past. The dishwasher drained into a standpipe below the floor the floor with a p-trap under it connecting it to the main waste pipe. It has no vent other than where the main waste line turns up the wall to vent through the roof about 6' horizontally above where the p-trap connects to the main waste line.

The kitchen is a U shape, so the drain pipe has to run through cabinets and a 90-degree turn to get to the sink...I'd rather not do this. Attached are 3 options that I came up with...1)Leave as-is and reinstall dishwasher like it was before; 2)Leave trap as-is and extend standpipe up through floor as high as possible, or 3)Completely redo piping for dishwasher drain. Thanks for any help.

 

[hj]

#2, (right hand one), will work, but #3, (bottom one) is best. Do NOT connect the DW drain directly to the standpipe, unless you have an air gap in the counter top.

 

[Sponsor]

 

[cds0020]

Follow-up question - Instead of changing the existing piping, I may just run the drain line to the sink. The sink is a 48" corner cabinet plus about 3' away from the dishwasher. So I'm looking at about 6' or 7' of drain line to get there. Instead of going through the cabinets, would it work if I took the drain down through the floor and ran under the floor joists in the crawlspace, then back up into the sink cabinet? I would probably use CPVC through the crawlspace if I did this.

 

[Reach4]

Instead of going through the cabinets, would it work if I took the drain down through the floor and ran under the floor joists in the crawlspace, then back up into the sink cabinet?

No.

I am not a plumber. I would go with number 2 except that I would extend the pipe to only 42 inches above the under-floor trap arm. I don't know why a maximum might be important, but I read there are codes that have maximums of 30, 42 and 48 inches. So 42 seems like a medium choice.