Using a single pipe off the main drain for a washer and utility sink, venting?

Question

I am renovating my bathroom. I am using this as an opportunity to additionally:

1. Move my washer and dryer from the mudroom, into the garage.
2. Add a utility sink to the garage.

The current plumbing

Here are is my washer and dryer (which will be moved), located on the other side of the pictured wall.

Here is my toilet. It isn't being moved, I'm just being informational.

The new plumbing Here is where I'd like to move the washer and dryer, on the other side of the pictured wall (in the garage).

Here is where I'd like to install the new utility sink. Again, on the other side of the pictured wall.

Here is what I'm thinking about the piping.

Notes:

• I will use the existing T-connection that the old washer drain is hooked onto.
• The piping will turn 90-degrees through a load-bearing wall. The right wall is 2x6, the left is 2x4.
• The piping will elevate 1-inch every foot as it comes off of the main drain.
• The current copper supply line for the washer will be refitted to supply the new washer location and utility sink. I'm not concerned about water pressure issues when both are active.
• The P-trap for the utility sink will be outside of the wall (in the garage).

Some concerns:

• Should I be concerned about the velocity of the washer drain siphoning out the P-trap of the utility sink?
• Someone mentioned I could use a single line off of the main drain pipe for both the washer and dryer, but only if I add a studor vent. How exactly would I apply it? Outside the garage on the utility sink? Just before the pipe goes into the wall? So when looking at the utility sink from the garage, I'd see "sink -> p-trap -> studor vent -> wall"? Will the studor vent allow enough air to be sucked in to protect against the negative pressure created by the velocity of a draining washer?

Answer 1

It is really a shame no one answered you, as this was a well organized thoughtful question with plenty of pics.

I’m sure it’s too late, as I saw your other q, but for future reference:

1. the correct solution is/was to run a 2” drain to the laundry with stand pipe no longer than 42” above trap weir. The pipe should use roughly 1/4” per foot pitch. The pipe should be as low as possible because…

2. The slop sink should have a 2” sanitary (not 90) behind it, that drops down into the now-below horizontal drain for the laundry. The san T should go straight up to above the height of the sink/laundry overflow…

3. THEN 90 the vent and cut through your studs, around the corner and over to your main vent stack. Note: you could bring it to the ceiling then use a soffit or dropped ceiling to get it over to the main vent instead of cutting more giant holes in your wall framing :)

Now you are wet venting the laundry through the sink drain. This is permitted by upc. The slope after the sink/vent is not as important, though if you make it some weird slope, it can cause issues so stick with 1/4” pf for horizontal runs.

Note that ideally you do not cut load bearing walls as much as you will need to to fit 2” pvc, but i am not a carpenter so I don’t care. Jk but seriously I don’t have any good ideas for you on that one.

Hope the project worked out!