I would like to install a utility box in the wall for my washing machine to drain into instead of the sink next to machine. Can I just run my drain pipe straight into existing drainline running along the joists in floor. The main 4" vent is 20" from proposed work? Sorry about vagueness never have done new plumbing, have only replaced old stuff.

Thank You,

Chris

You need to have trap on the new drain pipe. The pipe should be at least 2" or even 3" and should be at least 30" tall.

I just had plumber out to estimate and he told me he has to tie into a vent stack is this true

Did he mean he needed to install a vent for this drain or was he draining into the vent. I think your existing drain line is already vented but he may be creating a wet vent.

The drain for my bathroom sink has a loop created I assume for venting and he wanted to tap into this loop for the new drain. So to answer your question he is draining into the vent. What is a wet vent?

The vent is usually inside your wall and runs all the way up through your roof line. It allows air to get sucked into your drain pipes so the water can drain without gurgling or chugging. In some situations you can connect a drain into a vent , its then called a wet vent. We are actually getting a bit beyond what I normal do so maybe one of the plumbers will also step in. "bathroom sink has a loop " could you explain this a bit, is it a loop or a J or S shape in the drain pipe?

Bathroom drain extends up about 1' above inlet then makes a "U" and goes straight down.
Both vertical pieces of pipe then attach to horizantal pipe to exit house I am talking about just the pipes that are in the wall

Does it look like this trap Replace a P-Trap | Charles and Hudson or does it go to the floor instead of the wall?