100ft drain line to garage

[Phil P.]

I'm investigating adding a bathroom to our detached garage / workshop / outbuilding that's just about 100 feet away from the house. The elevation change is my concern. If I start a 4" drain line 24" deep at the garage and go 1/4" per foot I wind up 48" deep at the house where it will tie in to our house waste line. The waste line is only 36" down, so somewhere I need a pit and a pump.

Is it usual to bury the pump that deep (about 6ft I think to get pit below the 48" line)? Or is placing the pump at the outbuilding an option, then running the 2" pumped line back to the house 24" deep the whole way? I'd be digging in the crawlspace for tie-in so 6ft seems pretty deep!

I'm at the initial exploratory phase but if someone can advise the "most preferred" way to do this I'd greatly appreciate it.

 

[Dj2]

Before you make a decision, find out:
1. How deep your main line is where it connects to the city sewer.
2. Whether you need a permit.

In my city it's about 8' deep, making a project like yours possible.

 

[Sponsor]

 

[Reach4]

These threads may have some useful info.

https://terrylove.com/forums/index.php?threads/when-to-use-grinder-vs-sewage-ejector-pump.41632/
https://terrylove.com/forums/index.php?threads/long-distance-bathroom.57249/

 

[hj]

In cases like that, I have start ed the drain line 8" below the ground level in order to make the connection, plus 4" can be installed at 1/8" per foot grade.

 

[Phil P.]

Thanks for the prompt replies guys. Those links were helpful too. So I guess I need to get into the crawl space and dig on down to see how deep the line really is -- I guessed 36" but truly I'm not sure. Maybe if I find a clean out I can use some sort of dip-stick technique to figure it out.

I will need to get a permit. This is a small city and it would be hard to "sneak it in" especially because the city will LOVE to charge the fee for a new bathoom set. I see the inspector from time to time .. with your info I'll touch base with him to see what he has seen done around here and what works best.

If I do put the pump/grinder out in the workshop, then I just run a 2" line horizontal 24" deep (frost line here) the 100 feet over to drop in to the main house waste line right? I wasn't sure if waste (even ground up) could/would flow horizontal that distance. Phil

 

[hj]

Drain lines do not have to worry about "frost line" because they are NOT full of water.

 

[Phil P.]

So I spoke with our building inspector this week and he confirmed the usual way to do this around here is to install the pit and pump at the workshop and them pump it back 100 feet to the house and tie in to the drain line. So if this line is 24" down as it enters the crawlspace, is there any problem bringing it back up above ground to tie in to a stack and vent? or best to dig down to keep it "mostly level" as it dumps into main waste line? I do think this design would leave the pipe pretty much always full from the clapper valve all the way to the house. If I dug down much of it would drain/empty by gravity. Any preference or big plus/minus to doing one or the other (except less digging bringing it up above ground in crawlspace -- not my favorite place to dig

 

[Jadnashua]

I would really try to make this all work via gravity as a pump and pit are a nuisance, and really a pain when it comes time for maintenance.

As was said, a 4" pipe can get by with 1/8"/foot slope, but you must be very careful to keep things properly bedded, as any sinking can cause a flat or belly, and then you'll have issues.