PVC Main Drain Design Questions

[Joseph Skoler]

I'm renovating a house and I sure could use some help from a pro.

I have a 6" PVC pipe going from the house to the septic tank.

In the house, the main drain needs to go (all in a horizontal plane) along one wall about 20', turn 90 degrees, then go along another wall about 35' before turning up.

In addition, this main drain will serve 3 small guest cottages. That pipe turns the opposite way on the wall it enters the house for about 10', turns 90 degrees, goes about 25' and then turns 90 degrees to back out of the house (again, all in a horizontal plane)

I'm thinking continue with 6" PVC until the pipe turns up into the house and until it out to the cottages.

Here's a drawing looking down.

I understand I need a good pitch (1/4" per foot?). Will that be enough? Do I need additional cleanouts?

Can I simply use a Sanitary Tee where the pipe enters the house? I am concerned about sewage going straight across the Tee instead of turning and going out.

Any and all suggestions are very much appreciated (and needed).

 

[Reach4]

I understand I need a good pitch (1/4" per foot?). Will that be enough? Do I need additional cleanouts?

Can I simply use a Sanitary Tee where the pipe enters the house? I am concerned about sewage going straight across the Tee instead of turning and going out.

1/8th inch per foot is enough with 6 inch.

A sanitary tee for waste can only transition horizontal to vertical. Otherwise use 45s (or shallower), wyes, long sweep 90 , and medium sweep 90s. Consider routing pipes underground around the house as an alternative to taking basement space. A quarter bend is 90 degrees, and an eighth bend is 45 degrees.

Find IPC Section 708 Cleanouts. I am not going to try to interpret it for you.

UPC requires a cleanout if you turn more than 135 degrees IIRC. Not your rule, but sounds like a good idea.


Also drain serving a house can be 3 or 4 inch, and then transition to 6, maybe in the yard on the way to the septic tank. I am not a pro.

 

[Sponsor]

 

[wwhitney]

If the stack on the left is 4", what is the point of running 6" horizontally in the basement from there to the exit to the septic tank? Seems like it could be 4" as well, at least until it meets with the drain from the cottages.

What's the upside on running the cottages' sewer through the main house basement, rather than connecting to the 6" septic sewer outside the house?

To answer your question, a san-tee is definitely not allowed. If everything stays horizontal, you need a combo for one side, plus a LT90 for the other. You could also use two combos to have a cleanout. That geometry makes it impossible to get both side the same distance from the wall initially, but the right side is going to turn along another wall anyway, so that shouldn't be an issue. If you wanted to cut the corner on the right, you could use a 45 or wye instead of the LT90 or combo.

If you're willing to use up some height, you could bring the two sides in higher than the exit to the street. Then you could use a double wye vertically (or 45 degrees off vertical) with 45s on each side inlet to join the two sides together, with the top being a cleanout. Then a LT90 (or a 45) on the bottom to turn back horizontally. But in 6" that might be a lot of height.

I had some more complicated suggestions, but per Charlotte's catalog, fitting selection in 6" is limited.

Cheers, Wayne

 

[Jeff H Young]

No Idea scope of work but there could be many reasons for leaving the tie in to cottages under the house. The biggest reason being perhaps no excavation is planned out side ?
1/4 inch per foot fall is good , I might give a few inches more on a long run.
I would expect 4 inch would be plenty big for the entire project .
Is this the current situation with both drains coming into the main house? or a new idea? Any Idea why there is or will be a 6 inch line?

 

[Mr tee]

4" is big enough. The way you show the tee where it exits the building toward the septic is wrong. You need wyes/combos.

 

[Jeff H Young]

Evidently he has a 6 inch now . Asking for help but I can't tell if OP already has existing piping inside coming from the guest cottages If he is replacing all the lines outside . hopefully he was just showing his basic idea and not going actually pipe it without wye type fittings

 

[THESHACK]

Be careful of too much slope. Anything 4" and bigger is typically 1:100 (1/8 per foot). Too heavy a slope and the liquid out runs the solids leaving the solids to build up in the pipe. As mention by Mr Tee you need wye's at the septic connection. I'd run an LT 90 into the straight portion of the wye from one leg and connect a 45 to the wye inlet for the other leg. Make sure all your 90's are LT's as well

 

[Joseph Skoler]

Thank you all so much for your help!

1) 1/8"/ft is enough; 1/4"/ft is better. No more than that because the liquid will fall out faster than the solids.

2) San. Tee only for horizontal to verical changes. All other fittings seem to be fine for any other direction directions.

3) Cleanouts good.

4) 4" vs. 6": Seems like all you pros would use a 4". I already have the 6" and the sleeve installed through the 24" thick concrete basement wall (100 years old), so I'll stick with the 6" from house to septic tank. As for when to reduce to 4", my thinking (which is often wrong, so I wouldn't be surprised if is now) is that 6" is better (less of a chance of a clog). That's how I come to make all the horizontal runs in the basement 6". Maybe even use 6" elbows/tees/cleanout and make only the verticals 4". Does that make sense?

5) The cottage drain line comes into the basement of the house instead of the connecting outside because (1) connecting outside would require the sewer line and water line to cross each other (and I don't have experience doing that correctly) and (2) the cottages are almost on the opposite side of the the house from where the septic tank is, so the path would be tricky.

6) There is no current situation -- only my inexperienced ideas. So, I'm not clear on how to come off the 6" main and go in 2 opposite directions. Should I use an elbow to up up and then a tee on top of the elbow? Or a double wye with a cleanout on top? I'm not clear how the wye should best be oriented.

Other than what I'm not unclear about, did I get any of that wrong?

Thank you!

 

[Reach4]

Should I use an elbow to up up and then a tee on top of the elbow?

Combo (combination of a wye with 45), with the straight line a cleanout.

Or a double wye with a cleanout on top?

That would only work if you ran the center output thru the sill plate and had the cleanout outside. That seems popular in warm areas, but not in cold. Maybe it is an insulation thing.

I'm not clear how the wye should best be oriented.

You are asking if a cleanout should be sticking out of the side down, or horizontal, I think. I had to think about what you were asking. Down is going to catch passing solids.

Incidentally, there are some that think 3 inch is better than 4 because of higher velocities. I have no insight into that.

 

[Jeff H Young]

thanks joseph for the extra info enter building building with 6x 4 combi or wye on end of 6 inch will be c/o 4 inch line goes toward the cottages a foot or so from the junction put a 4 inch combi on back the branch pointing up goes to main house so short piece and a santee on top for cleanout the santee will be pointed 180 degrees. and so on . I dont know how much height you have to play with bettween the 6 inch core and the core in wall for cottages therefor that section just gets sloped and you can offset when needed.
1/4 perfoot slope is normaly the minimum slope My code only allows 1/8 per foot only with inspector aproval on 4 inch pipe. pipe often bowed If you run on the bare min and inspector finds a flat spot it isnt good So I give a little more than the minimum and dont feel that compromises the build.

 

[Jeff H Young]

wanted to add about what reach 4 brought up.
I don't know how much to believe that oversizing helps or hurts a 6 inch for house I am guessing offers zero benefit and possible negative . but not getting enough water to kind of flush it out isn't good.
If there is an existing 6 inch I wouldn't sweat but not expecting any benefit. closely following code your allowed over 200 fixture units on 4 inch so I'd feel safe with 4 inch. the cost of 6 plus glue and working with bigger pipe is harder . 4 inch should be fine for 3 cottages I'd think I'd run with 4 inch it should be a little easier to service maybe a drain guy will give his 2 cents I like 4 inch outside the building .

 

[Joseph Skoler]

Reach4 and Jeff -- I so very much appreciate your generosity with your expertise. And I so very much wish I could put it to good use.

But, I'm afraid it is way over my head (despite my attempts to understand).

I understand that changing from 6" to 4" as close to the location where the pipe exits the house is recommended -- and I will follow that advice.

What I'm struggling with grasping is how to arrange and orient the fittings to have the house's waste and the cottage's waste (each coming from opposite sides of the 6" main drain pipe) to come together and connect to the 6" pipe.

For example, with the 6" pipe coming through the basement wall (horizontal), what is the first fitting (a sweep elbow pointing up or a 6x4 combo wye with cleanout facing the center of the basement (i.e., in the same direction and both vertical and horizontal plane of the main 6" pipe)?

Something like the attached attached directly to the horizontal 6" pipe? or a sweep elbow pointing up and then this double combo wye?

Thank you!

 

[wwhitney]

The double wye shown in your last picture is available as 6x6x4x4. So the center path would be 6" and the side branches would be 4". That would work well for you to have a 6" cleanout and two 4" drains coming in, one for the cottages, and one for the main house.

As to the orientation, it depends on the height you have available between when the 6" exits the house, and where the 4" from the cottages enters, or where the 4" for the house comes down from above. You need sufficient slope on your horizontal segments.

The minimum height option is to use the double wye flat (the barrel should be at least 1/4" per foot sloped). That's a little tricky because you have to get the two sides at exactly the same elevation, otherwise one side branch will have too little slope. Not sure if having the cleanout flat is good for access, or possibly negative for trapping backwash. Others may have an opinion on this arrangement.

But since you are putting 45s into the two side inlets of the double wye, you could use any elbow you want between the double wye and the 6" exit, assuming you can afford the height. A 22.5 will give you a little slope so the left and right side don't have to be perfectly even. A LT90 might be too much, as far as the cleanout being accessible, or it might be good, as far as wanting the house run to be tight to the bottom of the joists at their upstream ends.

Cheers, Wayne

 

[Jeff H Young]

if the hole in wall allows you can 90 up and use that double wye. I would just use a single wye on side though toward cottage. too hard to explain

 

[wwhitney]

P.S. Thinking about it a bit more, I would assume the cottage sewer elevation will be controlling your choices here. I.e. how long is the horizontal run between the 6" exit to the septic at the house and the farthest cottage's building drain exiting the cottage? And what is the highest that building drain can be, relative to your 6" exit to the septic at the house?

E.g. if the total cottage sewer run is 200', that's 50" of fall if you go with 1/4" per foot. If you have a 60" elevation difference, you've got 10" of elevation change you can use somewhere, maybe for the connection discussed in the previous post. If you have 50" to start with, you'll want to keep the cottage side horizontal throughout your house basement. And if you have only 30" to start with, then you need to start looking at running the cottage sewer at 1/8" per foot, and what that requires.

Cheers, Wayne

 

[Jeff H Young]

Joseph , are the holes already in the wall? are you running a complete new system or just in the basement? if a new system the holes in wall dictate elevation and limit the allowable slope

 

[Reach4]

6x4 combo wye with cleanout facing the center of the basement

That one. Gives you the cleanout, and uses minimum low wall space. Then maybe a wye and 45 going left with a medium to long sweep atop the wye going right (or switch left and right). Or maybe a 4 inch double elbow up high.

 

[wwhitney]

Those are good options if the height is available. We don't know what's going on with the cottage sewer.

Charlotte, at least, doesn't make a 4" double quarter bend, they stop at 3".

Cheers, Wayne

 

[Reach4]

Charlotte, at least, doesn't make a 4" double quarter bend, they stop at 3".

Spears P327-040

A double combo with the top center port plugged could be used I think.

Joseph , are the holes already in the wall? are you running a complete new system or just in the basement? if a new system the holes in wall dictate elevation and limit the allowable slope

Great point. The cottage drain will not be able to go up to the joists. So a solution that keeps the cottage drain low is probably needed. It sure would be nice if that cottage drain could join the flow in the yard, instead of having to travel thru the basement.

That 6x6x4x4 in #12 might be the best deal, with a long spigot sweep (or 45) into the left port, and a pipe in the other might do it. The horizontal right port connecting to the cottage could be properly sloped, and the main house drainage would only have reverse slope for a very short distance. OK?

5) The cottage drain line comes into the basement of the house instead of the connecting outside because (1) connecting outside would require the sewer line and water line to cross each other (and I don't have experience doing that correctly)

I think that could be dealt with.

https://codes.iccsafe.org/content/IPC2018/chapter-6-water-supply-and-distribution says

603.2 Separation of water service and building sewer.
Where water service piping is located in the same trench with the building sewer, such sewer shall be constructed of materials listed in Table 702.2. Where the building sewer piping is not constructed of materials listed in Table 702.2, the water service pipe and the building sewer shall be horizontally separated by not less than 5 feet (1524 mm) of undisturbed or compacted earth. The required separation distance shall not apply where a water service pipe crosses a sewer pipe, provided that the water service is sleeved to a point not less than 5 feet (1524 mm) horizontally from the sewer pipe centerline on both sides of such crossing. The sleeve shall be of pipe materials listed in Table 605.3, 702.2 or 702.3. The required separation distance shall not apply where the bottom of the water service pipe, located within 5 feet (1524 mm) of the sewer, is not less than 12 inches (305 mm) above the highest point of the top of the building sewer.
​

As I read it, you could lay a single 10 ft piece of PVC centered and at right angles above the sewer line, and route the water supply pipe through that. With a longer length, you would not have to be as careful with the angle or centering.


https://codes.iccsafe.org/content/IPC2018/chapter-7-sanitary-drainage has table 702.2. Your materials will be in the table, at least the new stuff will be.

 

[wwhitney]

Spears P327-040

A double combo with the top center port plugged could be used I think.

Nice find on the Spears part. The analogue of a double quarter bend would be a double san-tee with the center port plugged (or as a cleanout).

That 6x6x4x4 in #12 might be the best deal, with a long spigot sweep (or 45) into the left port, and a pipe in the other might do it. The horizontal right port connecting to the cottage could be properly sloped, and the main house drainage would only have reverse slope for a very short distance. OK?

I wouldn't do that, you don't want any flat spots. If you want to install a double wye horizontally, then I say just make sure that it is dead level side to side, and that the barrel has a slope at least 41% more the minimum allowable side inlet slope. If you don't have confidence you can get it dead level side to side, then increase the barrel slope to provide some margin of error.

Cheers, Wayne