Laundry Room Standpipe - trap required?

Hello everyone,
I am in the process of redoing the layout of my laundry room (home is about 17 years old in whitby ontario) and was looking at the the existing plumbing for the washing machine.

My question relates to the p-trap. Does the standing pipe require a p-trap?
The laundry sink is nowhere near the washing machine so it does not feed directly into that line but it comes straight down into the basements, connects to an elbow joint proceeded with a long straight run that feeds into the stack via a y-attachment.

With my investigations I don't think I saw any trap coming into the basement however i didn't look inside the walls.

I can post photos if anyone thinks they will help.

Thanks!

If it did not have a trap, there would be NOTHING to prevent the sewer gas from coming back up the standpipe.

cacher_chick said:

If it did not have a trap, there would be NOTHING to prevent the sewer gas from coming back up the standpipe.

Click to expand...

That's what I figured

The trap is usually in the wall, it joins into a stack then drains down from there. It would need to be vented as well.

Rule of thumb is in the civilized world, every drain must have a trap and be vented. Your toilets have a build in trap, everything else has to have one added.