Hello all, new to the site. We are roughing in some simple drain line for a toilet and sink in a new barn slab floor. We are using 3" drain running to a septic tank. Is it ok to vent the drain "upstream" apprx. 4' from the toilet where the sink will be located? It is a straight run from the sink drain to the toilet, using a 1/4" per foot slope.

Hi Fennicip:

It may be better to run the 3" directly to the toilet...branch of that 3" with a 3"x2" wye and pick up the sink drain. Run the pipe out of the ground using a 2" 45 cemented into a 2" street 45 (makes a long sweep 90) and pick up the sink at 18" to center off finish floor and run a 2" vent up and through the roof (1st image)

You have now vented the sink AND wet vented the toilet. This is acceptable standard in most of the country. however, it is always a good idea to confirm that wet venting is allowed in your area.

You may also want to check to be sure that your local inspector will not require you to treat this structure as a separate building... if he does you will be required to run a 3" vent up and through the roof (2nd image).

Are you installing a main drain cleanout within 18-24" of the inside or outside of the barn? Let me know.

MARK

Thanks, your first diagram is what I am doing but it is 3" from the sink to the toilet also, with a cleanout 24" upstream from sink drain (that is 2" tied to a 3" Y) and one outside the barn about 24" downstream, just in case.