I am installing a brand new 4" sewer line in the basement leading to city hook up.I have dug a trench almost 90 feet long sloping toward the street hook up. My question is, how do I maintain and determine the slope of 1/4 inch per foot on a ninety foot run? What do I fill up the trench with where the line is going to rest? Kp.

On anything larger the 2" you can go 1/8 to the foot . I find that a 1/8thn bubble on my level gives me the slope I need. You should end up with 11 1/4" of fall going 1/8th. To the foot. Instead of then 22 1/2" you'ud have at 14" to the foot.
Good luck, Tom

As Tom pointed out, an 1/8" pitch per foot of 4" pipe is accepted and allowed by all plumbing codes.

Your cheapest bet to establish and maintain your pitch would be to purchase a 4 foot level and then wanting an 1/8" pitch per foot of pipe tape a 1/2" block of wood onto one end of the level. Then, use this level by putting it on the pipes and maintain LEVEl reading all the way to street hook up. In this manner you are guaranteed to have perfect pitch!

They sell PITCH LEVELS (see image of an older model pitch level), but my way is muchhhhh cheaper for you... ;)

If you decide you want to keep 1/4" pitch, just tape a 1" block of wood to the 4 foot level, right?

In terms of bedding materials... well tamped sand and pea gravel both work well!



Mark

For best accuracy on a line 90 feet long, you need to establish a stringline as a reference or use some of the more modern laser instruments. How did you determine the grade for the 90' of trench you have dug? The bottom of the trench should have been based on the flowline of the pipe and the depth of the bedding material. Then your bedding is close to the right grade and you can adjust as you lay the pipe. You can't start laying the pipe at the high end (house), then leap frog along with a 4' level and hope to be accurate at the point of tie-in, in my opinion as a pipe laying highway engineer. How deep is your trench and is it safe?

As a pipe laying highway engineer I think you are blowing this 90 foot run of pipe wayyyy out of proportion, Smearcase... ;) It is only 90 feet... not miles of pipe being inspected by a state highway engineer/inspector!!

Ya got to figure that if the trench has been dug reasonably well and he begins AT THE MAIN DRAIN in the street itself, he's going to be just fine... add a little, remove a little, but overall a 4 foot level (pitch level) as I provided does as good a job as a laser level (yes I said that)... and I'm just saying that as a plumber that has used this many (many) times!

However, with that being said, I have also used laser levels and other instruments and certainly can't disagree that a laser level is a great instrument that would also end with perfect results!



Mark

I won't argue with you. But we placed plenty of sewer lines as part of road projects and had to engineer them all. You well-experienced guys can probably do a good job with the 4' level method but a novice needs to know where he is going to end up before he starts. I wouldn't dig a 90' trench by hand, and certainly not by machine not knowing what depth I was supposed to be down to. Get the bottom of the trench right the first pass, lay the depth of bedding you need, and laying the pipe is a piece of cake.
I could set up a stringline in about 10 minutes.
I'll ask again - how did he know how deep to dig the trench at say the midpoint? Just digging a constant depth? Works fine if the slope of the existing ground is the same as the pipe will be. Maybe he has nice flat ground and maybe he doesn't- I can't tell from the question.
Very unusual to encounter miles of pipe in one run on a highway project.
In fact, 90' ain't a bad average for a culvert crossing under a road.
Maybe miles of pipe In closed systems but they are laid in smaller segments from manhole to manhole. They had to be on the money or they ended up in the roadway stone section or hit another utility they were crossing.
I stand by my answer for this situation.

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You can't start laying the pipe at the high end (house),]

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SAY WHAT?

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In my opinion as a pipe laying highway engineer

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You may be a high falooten engineer but you sure haven't plumber many houses. Let me show you how a plumber runs a sewer line starting at the house cleanout. We lay a length f PVC down in a trench and give our level a 1/8th bubble. We maintain that pitch all the way out to the curb where we connect to the city raiser. Because the raiser's lower we 45 down to pick it up. That's how we do it. No 90 foot string that will sag or laser, just a level and common sense.
Smearcase, You may be a smart dude but it's very clear to me that your no plumber. My advice? Stick with what you know best and leave the plumbing questions to us. Regards, Tom

I claim no plumbing expertise. I have learned a vast amount from you guys over the last five years, and I appreciate that.
But you have to have a trench to lay that first piece of pipe in, that is somewhere close to the correct grade and if you have knolls and dips in the yard like mine I do it with some simple engineering (the only kind I know how to do- never claimed to be high falutin). I mentioned intermediate stakes I believe. I don't try to stretch a stringline 90'.
You guys are used to working with these conditions. I realize that. I don't know the poster's level of expertise or the lay of his land. I am trying to avoid him starting to lay pipe and realize that he is too shallow and have to dig deeper, or too low and have to fill under the pipe and end up with a sag in the line that you guys are frequently giving people advice about.
I'll continue to comment on trenches which I have a lot of experience laying out and excavating.

I think your information adds to the discussion here, Smearcase, but yeah we seem to approach things differently.

Here, just as an example, if a homeowner (or plumber) has hired a backhoe operator and they dig the trench you aren't going to tell them much of anything when it comes to digging the trench... that's their job and they are usually very good at it and get insulted quickly when you try to interfere with it. In most cases I've been involved in, these backhoe operators don't need any lasers/tools or anything to comb a nice trench for us to work in... just a fact in most cases!

In terms of a homeowner digging a 90' trench by hand, well, let's just say that you can almost always be sure it will be to thin (like 6" wide) and yeah, bellies everywhere, for sure! In these cases, they usually find out quickly that there are 3 foot rocks in the way in terms of both depth and width of the trench and end up hiring it out anyway, huh? Then, the pros come in and widen the trench and use levels, lasers, etc...

Anyway, again, your information is very helpful here in that it has allowed us to present a well-rounded discussion on this topic for future homeowners... certainly the reason we are here to begin with!

Have a good day!

Mark

I agree 100%.
Enjoy what's left of Thanksgiving weekend.

Seems you have air in your system. Go to home depot and purchase and install an air arrest-or that helps eliminate air from the lines. There are several versions available that helps from pipe knocks. Kp.