# Seeking some advice on dry fitting PVC pipe

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#### Branimal

##### New Member
I'm dry fitting some 3" PVC pipe and need some advice on how to get the sizing right. Most of my experience is from working with no hub cast iron. With NH CI, if I get the sizing on pipes or rotations on fittings wrong I can easily redo my work without throwing out fittings & pipe.

My biggest issue with PVC is when I'm dry fitting the pipe doesn't completely seat into the fitting. This throws off both my fitting angles and my pipe lengths.

I'm trying to join these 2 street 45*s with a length of pipe. Red arrow. All the other sections of PVC are only dry fit unless noted.

#### Terry

##### The Plumbing Wizard
Staff member
You can't dry fit PVC or ABS fittings. They won't slide in all the way unless there is glue on the pipe and the hub.
Measurements are done by measuring the inside of the hub and doing the math on that. It helps to be spatial.

#### wwhitney

You can't dry fit and then expect to use those pipe segments in your final glue up. But you can dry fit and get all the fittings in the places you want them with the orientations you want. And then carefully measure the distance between fittings from hub to hub, and cut new pipe segments based on those measurements.

I.e. if in your dry fit of 3" fittings you end up with a 6" exposure of pipe between hubs, you'll need a 9" final piece of pipe, as the hub depth on each end is 1-1/2". For the dry fit you might have used a piece of pipe 7-1/2" or 8" long and only inserted it part way into the fittings.

To translate from exposed pipe length between hubs (on your dry fit) to final pipe segment length, you can just go off the catalog hub depths (1-1/2" = 5/8", 2" = 3/4", 3" = 1-1/2", 4" = 1-3/4") or measure the depth on your particular fittings (I have found some variation). Or for super precision if it's critical, you can do a test glue up using identical fittings. I.e. if you start with an exactly 9" pipe of 3" pipe and glue up two fittings on each end, you might find the exposed pipe length is 6-1/16" or 6-1/8", due to variations in the fittings, or your pipe cutting technique, or glue up technique.

Cheers, Wayne

#### Branimal

##### New Member
You can't dry fit and then expect to use those pipe segments in your final glue up. But you can dry fit and get all the fittings in the places you want them with the orientations you want. And then carefully measure the distance between fittings from hub to hub, and cut new pipe segments based on those measurements.

I.e. if in your dry fit of 3" fittings you end up with a 6" exposure of pipe between hubs, you'll need a 9" final piece of pipe, as the hub depth on each end is 1-1/2". For the dry fit you might have used a piece of pipe 7-1/2" or 8" long and only inserted it part way into the fittings.

To translate from exposed pipe length between hubs (on your dry fit) to final pipe segment length, you can just go off the catalog hub depths (1-1/2" = 5/8", 2" = 3/4", 3" = 1-1/2", 4" = 1-3/4") or measure the depth on your particular fittings (I have found some variation). Or for super precision if it's critical, you can do a test glue up using identical fittings. I.e. if you start with an exactly 9" pipe of 3" pipe and glue up two fittings on each end, you might find the exposed pipe length is 6-1/16" or 6-1/8", due to variations in the fittings, or your pipe cutting technique, or glue up technique.

Cheers, Wayne
Thanks Wayne - that's a great tip.

I used your method and quickly came up with something that works. I ditched the 45 sitting on top of the 3" wye and just rotated the wye. See pic. Everything is still dry fit.

The only tricky bit is connecting the last piece. Let's say the last piece is the length of pipe from the wye outlet to the 45 el higher up. I could glue the pipe to the wye first and then use the space the wye has off the wall to get the room to fit the opposing pipe end into the 45 el.

#### Reach4

##### Well-Known Member
For experimenting, you could sand off the sides of a pipe and a street elbow. A belt sander would be best, but patience and some fairly course sandpaper would let you experiment.

Of course those sanded pieces cannot be used in service. They are only for trial fitting.

On straight runs, you could add an extra cut and a shielded coupling to go make that rotatable.

But even better, look into the Charlotte ConnecTite® Push-Fit DWV fittings. They are like SharkBite push-to-connect, but for drain pipes. They cost a premium, but they could give you the flexibility and do-over ability that glued joints will not.

#### Branimal

##### New Member
Can I glue up both sides of that pvc pipe (see pic) at the same time? Do I have enough working time?

The directions on the cement say apply cement to the pipe then to the fitting and then again to the pipe. Doing this on both sides of the pipe within the working time seems tough.

Another option: This pvc run ends up attaching to a cast iron NH soil stack via a 4x3 santee via PVC/NH coupling, I could do the whole glue up and then hope everything lines up to the 4x3 santee.

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#### wwhitney

What would be best, of course, is to have a 3" joint you can glue up last for which you will still have at least 2" of axial play and a bit of lateral play (so you access the inner face of the hub). Then you can glue everything else up ensuring that joint remains dry fit, pop the joint open, apply primer/glue, and make up the last joint. Not clear to me given the geometry if you will have enough play in any of the joints, Failing that:

Another option: This pvc run ends up attaching to a cast iron NH soil stack via a 4x3 santee via PVC/NH coupling, I could do the whole glue up and then hope everything lines up to the 4x3 santee.
This is likely the best approach, I think. Do the glue-up of the final joint sufficiently close to the shielded coupling that you can confirm/hold the ends of the banded coupling joint in proper alignment as the glue sets. That is, with the shield off to the side, and the rubber of the coupling on one end of the joint, with the open end of the rubber coupling folded back on top of the other side of the rubber coupling.

The rubber coupling provides lateral play without necessarily providing axial play. So the above would work well if your last glue joint is rotational and lets you swing the pipe into the rubber coupling as you make up the joint. Or if you can get 1" of axial play at the coupling as you make up the last glue joint.

Cheers, Wayne

#### John Gayewski

Pipe is measured and cut using triangles and trigonometry. The three variables are run, offset and travel (these sometimes go by other names).

It looks like your trying to figure a rolling offset. These are a triangle inside of a triangle (kind of). Once you find the run and offset you'll use pathogen theorem to find the travel of the first triangle that travel is then your offset for the second triangle, the elevation difference will be the run. Then use the Pythagorean theorem to get your final center to center measurement. Then you take off the fittings. Glue a 45 onto that length of pipe then glue the other end into the wye and use your torpedo level to roll the 45 plumb or so.

Usually better to avoid a rolling offset unless you have help. Especially a long one.

#### Branimal

##### New Member
What would be best, of course, is to have a 3" joint you can glue up last for which you will still have at least 2" of axial play and a bit of lateral play (so you access the inner face of the hub). Then you can glue everything else up ensuring that joint remains dry fit, pop the joint open, apply primer/glue, and make up the last joint. Not clear to me given the geometry if you will have enough play in any of the joints, Failing that:

This is likely the best approach, I think. Do the glue-up of the final joint sufficiently close to the shielded coupling that you can confirm/hold the ends of the banded coupling joint in proper alignment as the glue sets. That is, with the shield off to the side, and the rubber of the coupling on one end of the joint, with the open end of the rubber coupling folded back on top of the other side of the rubber coupling.

The rubber coupling provides lateral play without necessarily providing axial play. So the above would work well if your last glue joint is rotational and lets you swing the pipe into the rubber coupling as you make up the joint. Or if you can get 1" of axial play at the coupling as you make up the last glue joint.

Cheers, Wayne
I got it setup and water tested with a garden hose. No leaks.

I ended up gluing the pvc pieces working toward the stack. I loosened the NH couplings on the CI 4x3 santee and was able to get some play at that location.

The last piece I need to install is the toilet plumbing. The plan was to run a piece of pipe and a long sweep 90. See pic. The other option is to run a wye and a 45. This would allow me to install a cleanout. But I have no idea how someone would be able to cleanout from that location.

I noticed that I wasn't getting quite the insertion depth I measured out. 1 1/2" for a 3" pipe. I think part of the problem is I'm cutting my pipe on miter saw. I didn't chamfer out the edges. Is sanded the square cut edges recommended? Also I didn't verify the actual insertion depth by test fitting a pipe to a fitting b/c I didn't want to burn a fitting. Next time, I'll test with a coupling.

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#### John Gayewski

Generally I measure and mark the pipe for the full dimension and then make my cut just short of my line that gives me pretty prefect fitting to fitting measurements. Generally the pipe works itself out of the joint a little unless you hold it for a really long time with a lot of force.

#### Jeff H Young

its a good idea and prcatice to break the edge inside and out the outside edge chamfered slightly with a knife a file or sanding just makes for a better job mostly un noticed but if your not in a hurry these prep steps will help reduce leaks my opinion even if largely unnesssesary

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