Septic line distance limitations

[5030tinkerer]

I will be building a new home and separate outbuilding this starting this spring. I'd like to put a half bath in the outbuilding. Does anyone know the feasibility of tying the outbuilding to the house septic tank? I suppose the real question is whether there is a distance limit I need to stay within for my drain pipe. I'd hate to have to put in two septic systems just for a convenience. /forums/images/graemlins/confused.gif

Thanks for any ideas,

Ed

 

[Bird]

Ed, I think I'd only be concerned with whether it was a distance that would permit me to keep a very slight downhill run to the septic system. Maybe someone else can refresh my memory; was it one inch or a quarter inch per 10' of lateral line? And there's another possibility also that you might consider, or talk to septic installers in your area. One of my brothers built a home on 10 acres and had one of the aerobic sewer systems installed at the time. Later, they fixed an RV parking site for the other brother to live on. The RV was about 75' from the septic tank, so the guy who installed the original system installed a 50 gallon underground tank with a macerator pump and a 2" line to the original septic system. Of course you'd have to wire the electric power for the pump, but it worked well for them.

 

[KentT]

I'm planning something similar, and hope to start construction soon -- it's still in the plans/blueprint stage. I'll be building a 2-car garage with an apartment over it, and a laundry room and 1/2 bath on the ground floor, to use a vacation cottage. Then, I plan to build a 3 BR retirement house a few years down the road, and connect the two with a covered breezeway.

I know of no distance limitations, as long as you can get sufficient grade, as Bird discussed. But, be sure to size the tank and field lines for the total needs of both buildings.

 

[5030tinkerer]

Thanks guys. TBN is truly awesome. Where else can you post a question before a late dinner and get a response when you get back to the ol' PC? I think I have the 1/4" drop per 10' run, but will verify when I get that far. For now, Bird has come up with an option that I hadn't considered that will surely work without a hitch. Am I correct in thinking that I'd want to bury that 2" line from the 50 gal tank to the main septic 42" down since a check valve just after the pump would possibly be keeping the line full all the time if it had to go uphill (or is there some other trick there)? The only concern that I would have about that is at the end of the 2" run (at the tie in to the 4" line from the house) since that would reasonably have to go uphill to make the connection. I suppose that I could just bury my holding tank such that the top is 42" or more down, thus requiring the 4" house feed line to be that low? Any drawbacks to this approach?

 

[inveresk]

I don't believe there is a regulation limit on lengths of drains to septic tanks provided you respect the 1 " 40 fall and have rodding eyes every 60 feet or so to clear blockages but you'll want to keep it as short as possible for maintenance purposes. The longer the run the deeper your drains will have to be in flat ground to get a gravity feed and there will be a limit on how deep you'd want to install you're septic tank.

The suggestion of installing a macerator by Bird is a good one that will ensure that any solids are at least part liquidised and if you can ensure a gravity feed to the septic tank, you shouldn't have much problems. Pumping is possible as well but best to try to design a gravity system first and turn to this option if gravity can't be made to work.

 

[TCarey]

Most plumbing codes require a minimum of 1/8" per foot of slope. That means every 96 feet of run, you will have 1 foot of fall. There really is no "limit" on the length of run, but you must maintain the fall. As mentioned earlier, every 75 feet code will require a cleanout be installed to clean the line if/and or when necessary.

If you cannot maintain the constant slope, you can go to a sewage lift pump and then you do not have to have that line at a gradual slope. The lift pumps will work OK, but anytime you can have a sanitary line drain naturally, you are better off than pumping.....

 

[PILOON]

Another option to consider is a second tank and a simple 'grey water' pump into 2" line feeding the drainage field.
That is if you have to go 'uphill'.
Such a pump is cheaper and easier to maintain than a solids pump.
I have 2 installations where I pump uphill as much as 25' to the drainage fields.
This is done in order to respect drainfield seperation from waterfronts.
Both pumping installations are reaching 20 yrs of operation.
Check valves are recommended otherwise backflow can actually damage the pump.
Usual installation calls for a greywater holding or pumping tank which can be even a large HD garbage plastic pail.

 

[tawilson]

I was at the plumbing supply house the other day, and they had on display a toilet setup with the pump built in. It's focus was on basement installations, but could be handy for many applications.

 

[Dmace]

Up here in NH, the rules are:

2% minimum slope from house to distribution box,
7% maximum unless you run a velocity reducer in the box, then it's 15% max.

There are no restrictions on length and the recommended pipe is 2" schedule 40 PVC pipe.

If you can't keep the pipe underground for the minimum slope for the entire length to the septic tank, then you could just gravity feed the line from the house to a 4x4 pump box. The box is 4' diameter and 4' deep, with a 1/3 - 1/2 hp effluent pump that pumps up to the d-box. There are limitations on length of a pump line, but that is all dependent on the head in the pump box and the friction loss in the line itself.

I have the charts for line friction and pump capacity if you need them.

I guess I should mention I am a septic designer also. /forums/images/graemlins/wink.gif

 

[EddieWalker]

I wouldn't use 2 inch pipe for draining anything but just water. If your running solids, as in a toilet, than use 3 inch line as a minimum.

Distance isn't an issue, but like everyone else said, drop is. You didn't mention how far this would be, but if you can tie into your existing system, than that would be cheapest and easiest.

3 to 7 percent is what I've always been told, but I wont' argue with 2 percent, but it seems on the shallow side.

I use a 6 foot level with a small piece of 2x4 taped to the end on it's edge. The level is 72 inches, so the 3 1/2 inch drop will put you real close to 5 percent.

How deep is the inlet to your septic? How far do you have to run the line?

If your 100 feet away, than your septic inlet needs to be between 3 to 7 feet deep with five feet giving you a nice 5 percent grade.

As for distance, the rule of thumb is to put cleanouts at just under twice the distance you can reach with a snake. My water utility is requireing me to put man holes in every 500 feet because they can reach 250 feet.

Will you ever have or need to dump an RV?

If you can, I like to have a cleanout on either end of the building so I don't have to take off the toilet to unplug a clog.

If you have to put in a collection tank and pump it uphill, there are kits to handle this. Allot of basements have this type of system. The size of the discharge pipe will based on the pump you use. I'd guess around an inch for what you need. My RV park will have a 3 inch line to handle the discharge for 300 RV's. Sewage under preasure requires a much smaller pipe than one fed by gravity.

Eddie