Greywater line - reducers?

Hello fellow permies,

When we built our house, we had a greywater line put in - there's a simple valve that determines whether the outflow goes to the septic or the greywater (of the entire house, yep, toilet too; got to love rural building inspectors, lol). The greywater line ends with a stub-out at the house wall, but it's time to plan for its actual use. We have a humanure toilet, which deals with feces, so that's good. I'm planning to only use the greywater line outside of frosty months, because Zone 5 and screw all of that extra complicated stuff to keep it all from freezing. It should still give us solid 6-7 months of not using the septic.

I have a few questions:
1) pipe size - in the Oasis book, the recommended pipe size is ~ 1.5'', to ensure that solids (food bits and such) aren't deposited on the pipe. Our stub-out is 3'', if I'm not mistaken - the regular size for sewage plumbing. How do we reduce the pipe without creating a clog spot?
2) pipe angle - we live on a hill. The greywater line will go into 2 swales at the bottom of the hill that have fruit trees and berry bushes planted into them. Our grade is higher than recommended in the Oasis book (although I'm not sure by how much). Does anyone have experience with grading greywater? How high can we push it without causing problems? I really don't want to have to dig down a lot to even out the grade...
3) toilet paper. Our current system is poo in the humanure toilet, pee in the regular toilet (otherwise we have an odour issue; Hodor?). We "let it mellow" to not waste flushing water. But that means a fair bit of toilet paper accumulating between flushes. I'm guessing a 1.5'' pipe isn't meant to deal with that. What would you recommend? Use a litter bucket to collect used TP after peeing (my partner will likely object)? Use cloth (again, likely object)? Flush more?

Thank you!

I've used a lot of gravity flow at my place, on the side of a hill for 25 years, and the best flow is down as straight and fast as you can do it. When you find yourself asking the question, "How far can we push it?" that's your warning question. I wouldn't do it, it will come back to haunt you. Sludge, food bits, and fats will collect in slow, low spots and cause plugs that then a heavy burst of water may knock loose, and then you've got the possibility of another block somewhere down the line. If liquid stays in these spots they will freeze and possible crack the line.

I know you don't want to dig anything, but I'll bet you will eventually have to, unless you can go around. Never put a 90 degree angle in a grey water line, only 45, so it can always move as fast as possible. It's better to dig it while you are excited about a new project, rather than have to keep screwing with it because it wasn't done in the first place....been there, done that.

I also wouldn't reduce the line. You are exactly right about paper not going through a small pipe. Someone will eventually not be willing to put the paper elsewhere, usually company, and it will get stuck in the worst of places. If anything else goes wrong, it will happen in a small line, and you'll have to hunt for where, then break into the line. Grey water has stuff in it, there's just no getting around it. We have a 4" pipe coming out, and I did reduce it to 3", and haven't had any issues with anything getting stuck (but we don't flush paper). We rinse all the big stuff off dishes and put it into a bucket that goes to the compost, then wash the dishes so small bits are the only thing that gets into the line, the way you rinse dishes before putting them in a dishwasher.

There are bark chip filters some people use before the grey water goes down the hill, just outside of the stub-out, to catch these things. But it isn't meant to catch paper or black water contents.

I run grey water into three plant- and rock-, and bark chip-filled tubs, so the plants help to clean the water up, particularly the high levels of soap. I wouldn't want straight soapy water going into my food, particularly berries that have a high water content. The plants in the bins are pond plants, and are doing well. The trick to keeping the mosquitoes out of these bins is to fill them with 3/4" rock and bark chips so the water level is just below the hard stuff, and runs out through a PVC pipe on the low end of the container. We should never use detergent in the kitchen or for laundry, always basic soaps, but I still wouldn't want them in my food.

Search on Reed Bed Filtration System and you'll see lots of examples. YouTube has some good ones.

In my compost toilet, we keep the paper separate and I compost that separately with about 3 times as much mowed weeds soaked with urine. I've got this mix in a tumbler, but I don't tumble it, because that bar through the middle leaves a huge hole in the pile, which is exactly what you don't want for compost. This tumbler was an early garden purchase 25 years ago, before I really understood why it wouldn't work, and I just try to find ways to use it. Once the tumbler barrel is full, which takes several weeks, I saturate everything again, then start tumbling it. The contents falls apart pretty quickly at that point and it's ready to go out, where I mix it with manure and compost.

To reduce a waste line, do it vertical or find an offset bushing.

I agree,don't reduce the size if the line. I spent two years augering 3" and 4" sewer lines.Even an otherwise perfect line that has a bow in it,too many bends, flat slope or reversed slope, will clog up.
And that's assuming only tp,bloody discharge and poop are flushed.

Sinks are almost worse to deal with than toilet lines because most if the waste we purposely put down them are fats and oils and these don't break down as easily as poop.

Maybe plant cattails in a filter basins and use their pollen etc as cover material in the composting toilet.

I think I just realized you mentioned you might do the occasional flush from the toilet out into the greywater line since they accidentally hooked it up wrong.  I don't think it's a good idea for several reasons.  The paper is awfully unsightly, it's sterile and takes forever to break down.  Urine brings in gnats like crazy.  Solid deposits should not be out where people, pets, or wild animals and rodents could step on them.  Tracking that stuff around is bad news, and it's really not the right way to handle the situation.   it all attracts flies and gnats.   I really would make an effort to undo the blackwater connection into the greywater line.  I think that's a mistake that makes a lot more work for you, and over time it could become a serious problem.  If you want to sell your house you'll need to disconnect the two anyway, and that kind of work never gets cheaper.  Technically the guys who hooked it up wrong should come back and fix it for free.  It could actually get you into trouble.

Thanks for all your replies. Apparently, there were a few misunderstandings:
1) I will NEVER put blackwater down the greywater line. The feces are dealt with separately in a humanure setting.
2) I was asking about having the grade of the greywater higher than recommended, not lower than recommended. I am aware of avoiding flat areas or saggy areas.

I'll think about using 3'' pipes all the way down, even if it's not recommended by the Oasis book. I hate having to change a tried-and-true recommendation though...

As for having the plumbers come in and fix it - all of the plumbing is below a concrete floor. I'm going to say that's not happening

S Usvy, urine and paper is considered black water, so that isn't supposed to exit the house unless it's into a septic tank.   So that's why urine going down that greywater line is not good, unless you set up a reedbed system that is contained and not allowing the liquid to touch the soil until it's been in the bed however long it's supposed to be there.  Canada has some municipal reed bed systems, so they've decided they are okay for municipal waste.  I'm not sure of all the requirements, but it is being done legally in some places.

I can see why you wouldn't want to tear up your cement to change that.  If you sell your house, or your house out-lives you, which it will, it will have to be disclosed  that it's hooked up wrong, and that is a serious code violation.  If you don't get those people back to fix the code violation they created, it becomes your responsibility.   New owners have to right to expect to be able to flush the toilet and not have it go out onto the ground.   If it's going to change hands,t you could just plug the whole thing up as it exits the house, and don't sell it with the greywater line feature.

I am curious about something - does Oasis recommend 1.5 inch as a minimum? Or does the author recommend 1.5 inch as the size to use? I am having some difficulty seeing where there would be a problem staying with the 3 inch pipe and can't imagine why he would recommend against it.

A bigger pipe and a greater slope is all good.
The water will be going faster,so precautions to prevent splashing or blowing out the woodchips.
Put at least one clean out into the line for inspection,or if necessary,cleaning.

Peter Ellis wrote:I am curious about something - does Oasis recommend 1.5 inch as a minimum? Or does the author recommend 1.5 inch as the size to use? I am having some difficulty seeing where there would be a problem staying with the 3 inch pipe and can't imagine why he would recommend against it.

Peter, I think the original question was talking about urine AND paper, and the paper would clog up a 1.5" line almost instantly.   When using bigger line than 1.5" on a greywater-only system,  I have had to put rodent-proof screen over the end, because they just can't resist pipes like that.   I've had gophers, mice, even little chickadees, the birds, get into pipes and get stuck.

Peter Ellis wrote:I am curious about something - does Oasis recommend 1.5 inch as a minimum? Or does the author recommend 1.5 inch as the size to use? I am having some difficulty seeing where there would be a problem staying with the 3 inch pipe and can't imagine why he would recommend against it.

Sorry for falling off the face of the Earth - went on a road trip in some more remote bits of Canada for a couple of weeks, and have been trying to catch up with life since coming back.
In the book, 1.5'' to 2'' pipes are depicted as having solids float or roll along in the pipe with the water flow. In tighter pipes, there's not enough air flow. In larger pipes, the fluid is not deep enough to make the solids float along. According to the book, at 3'', solids "roll along somewhat", and at 4'' solids are "an immobile island in thin flow". The 1.5'' recommendation is based on the flotation of solids in the greywater stream and based on cost.

So I'd think that we would either do a vertical reduction to 2'' or go with 3'' all the way (which would be more expensive).

Cristo Balete wrote:S Usvy, urine and paper is considered black water, so that isn't supposed to exit the house unless it's into a septic tank.   So that's why urine going down that greywater line is not good, unless you set up a reedbed system that is contained and not allowing the liquid to touch the soil until it's been in the bed however long it's supposed to be there.  Canada has some municipal reed bed systems, so they've decided they are okay for municipal waste.  I'm not sure of all the requirements, but it is being done legally in some places.

I can see why you wouldn't want to tear up your cement to change that.  If you sell your house, or your house out-lives you, which it will, it will have to be disclosed  that it's hooked up wrong, and that is a serious code violation.  If you don't get those people back to fix the code violation they created, it becomes your responsibility.   New owners have to right to expect to be able to flush the toilet and not have it go out onto the ground.   If it's going to change hands,t you could just plug the whole thing up as it exits the house, and don't sell it with the greywater line feature.

The urine regulation (if it's correct), feels silly - a lot of people use urine as a fertilizer; there are no bacterial issues of any kind there. I can see why the regs would be that way when it comes to toilets, maybe (to be on the safe side, what if someone does a number 2 in your toilet), but on the whole, putting urine together with blackwater is not right (in the grand scheme of things being universally right and wrong; usually has nothing to do with regulations ).

As for the disclosure or seal-off - yes, I agree. I wouldn't sell a house to anyone if they could flood their front lawn with poo water.