We have a barn in which we want to install a flush toilet (for human use). It is 53' from the home's septic tank.

Would it be better to install a septic tank near the barn to service the toilet and then run plumbing to the home's septic tank? If so, would we plumb to the drain lines after the home's septic tank or to lines leading to the home's septic tank.

If it matters, the barn is higher than the home's septic tank by approximately 70". Our frostline is 1'. We are in the foothills surrounding Tucson AZ and it makes nationwide news when it freezes here.

  • Well, if the usual 1/4" per foot slope requirement applies, you'd need 13-1/4" of rise over that distance. However, you also need to exit the barn below frost depth. You haven't mentioned what that is in your area.
    – isherwood
    May 27, 2021 at 20:12
  • Seems to me a 53' pipe is a lot less expensive (and invasive) than a new tank, but I'm not a septic expert. I'll let others weigh in. Of course, the capacity of your current septic is a factor. Have you looked into that?
    – isherwood
    May 27, 2021 at 20:34
  • Should be asking your local authority that you get the permit from, if you need another tank, not us. You are thinking of getting a permit aren't you?
    – crip659
    May 27, 2021 at 20:41
  • That's not a particularly long run for a pipe, properly sloped. My local authority would require an external cleanout access point ( they want a 50 foot snake to be long enough, so the extra 3 feet would be a trigger, and the actual pipe length (which is what they base this on, inclusive of the cleanout access portion for midline cleanouts) could easily be more than 53 feet.
    – Ecnerwal
    May 28, 2021 at 16:30
  • Why not just install a composting toilet? They work great and don’t require any of this extra headache. Can also hold quite a bit and have no smell or much maintenance. Nov 8, 2022 at 18:50

1 Answer 1


So much of this depends upon local regulations and soil conditions on your site.

If you decided to do a separate septic tank, you'd also need another drain field (in some parts of the country called a leach field). Seems like a lot of expense for a single toilet.

Next: Your existing septic system might not be regulated (licensed) for an additional device. In my neck of the woods, septic systems are sized and permitted by the number of bedrooms in the house. I DK how a toilet in a barn would count.

There is also the possibility of a hybrid system, where you install septic tanks near the barn and pump it to the drainfield.

But and as MUCH AS I HATE TO SAY IT on a DIY site, septic design and maintenance is coming under increasing scrutiny everywhere. You could probably do this off the record, and not permitted, but it will catch up to you eventually. Better to do it right the first time. You'll probably need to call a pro. Sorry!!!!!

  • In my area, it's also bedrooms - and the way a barn counts is that if it has no bedrooms, it doesn't count. Load is assumed to be based on the number of people living there (for residential purposes - commercial is a Whole other ball of wax) not how many toilets they have available to use. Thus, bedrooms.
    – Ecnerwal
    May 28, 2021 at 16:34
  • @Ecnerwal thanks for the comment. Number of bedrooms is kinda of an arbitrary standard, but I guess there's not much better. I grew up with 2 other brothers sharing a bedroom, technically it was a 2 bed room house, but 5 people living there. So I guess it's a crap shoot (pun intended)! May 28, 2021 at 16:40

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