Thanks, much appreciated. I was concerned with using the flexible fittings in a vertical application. They would have to support the pipe above it.

I think I figured this one out while I walked around at lunch. Some sources are $5 not $15 per copper fitting. And I think a plumbing supply house will sell copper pipe by the foot. All I need is 1 ft if I use the cut length from the original pipe, or 2 ft if all new. That brings it down to a manageable $30 or so for the task.

You would need to use some other method to support the upper section of the pipe. A clamp would not be difficult to come up with.

In my experience, plumbing supplys will only sell pipe in full lengths. You might find an agreeable plumber to sell you a foot or two.

Once you put an angle in the vent stack, it is not going to support very much weight above it (no more than a couple of feet). You have to strap it when it straightens back out. Usually, you would strap as close to the top ell as possible on your angled pipe, so that all the weight is transferred through the 45 to the strap, and none of it is on the other 45s. All of those will give.

Thank you for the information. I will strap the vertical pipe in place.

the pipe was not strapped in place by the builders. It runs from the basement DVW line vertically one story through the roof. Maybe codes were different or the builder was lazy.

If pipe runs straight up, it is probably not necessary to strap it. Since the weight of the pipe is transferred straight down. When you put a dog-leg in it, that changes, the weight above the dogleg is no longer transferred all the way down the pipe, only to the dog-leg.

Certainly all weight is transferred all the way down, even with a dog leg. This assumes flexible connections are not used. If flexible connectors are used, the upper part after the dog leg would also have to be supported, a real bother, so I will use rigid fittings.

You mean, the upper part might bend a bit to the side as the off-center weight bows the dog leg a little bit? Yes, that is true. Therefore, it is preferable to strap the dog leg closer to the top and ensure the center is blocked against a stud. The whole riser will be against a stud.

Certainly all weight is transferred all the way down, even with a dog leg. - This is both correct and incorrect. I oversimplified because seriously we don't need a physics discussion. There is simply greater force on the fitting at the dogleg, even if you were to recenter the upper pipe to find the true center of gravity the pipe entering the fitting will be under more pressure. In failure the joint will convert some of the mechanical energy to kinetic and thus take some energy off the transfer down.

This isn't rocket surgery nor am I going to get in a discussion with you about physics. Go to a big box store, get a few feet of copper pipe, 3 - ells, and a coupling. First, cut the pipes, put the coupling in and push strait down, next put a dogleg in and push straight down and compare the failure pressure.

In the end, I don't care what you do. I am no longer a plumber, much to the chagrin of my father who really wanted the "and Son" on the sign, so this is not professional advice and to be fair I only plumbed off and on for ten years, and haven't done it in over 20. So do whatever you want to do.