dwv plumbing

Yesterday, I started gluing together PVC pipes for the DWV system. This is the first time doing this, so things are moving slowly as I determine how best to do things and develop methods.

Attaching a pipe

From what I gather, typically some portion of the system is fixed into place with strapping or whatever it takes. Let's say a fitting is in place. Then the connecting pipe has one end placed into the fixed fitting, and the other end will be placed at the proper elevation such that the pipe is at a proper slope. This involves:
A. Supporting the pipe
B. Checking the slope of the pipe

These must be performed at the same time. For example:
1. Temporarily hang the pipe roughly where it should be
2. Check the slope
3. Adjust the hanger
4. Check again - if it's good enough, the support is correct
5. Go to step 3

This process is repeated as each pipe is attached, so we want to optimize it. That is, check the slope quickly, and adjust the hanger quickly.

Yesterday, I was running a tape measure vertically from the bottom of the pipe, and reading where my horizontal laser level crossed the tape. This would give a level reading from the reference laser. Given the length of the pipe, I can calculate how much the elevation should change, add/subtract that amount, and adjust the other end of the pipe until it meets that reading.

It's fast putting up the tape and reading the elevation. But it's slow to calculate the change in elevation to meet slope, it's confusing determining whether to add or subtract. It sounds simple, but seriously that was slow and confusing.

Today I'm going to try taking my bubble levels and taping on shims for the proper slope so when placed against the pipe it reads level. This is equivalent to using a plumber's level and I think this is how it's typically done. So now checking the level is simply placing the level against the bottom of the pipe and checking the bubble. This is a little slower than just reading elevation from the tape, but it's faster in that I don't have to calculate stuff. If I had a level that produced noise when it was level, I could strap it to the pipe say with velcro, and adjust it by hand just once.. I'll have to look into this.

Attaching a fitting

Attaching fittings is different from pipe, in that their relative orientation is important. For example, take a 90-degree bend. With one end attached to the pipe, the other end can swing around to point in any direction perpendicular to the slope of the pipe. Of course, it has a specific direction in which we want it to point, but the problem is getting it oriented precisely where it should go. Once it's glued, it's not moving.

This is a more difficult problem, and I'm still in the process of determining how to do this best. I believe this is achieved by working your way from fixed points (like where you drop from above at a lavatory/water closet drain) and hanging pipe to the junction, cut to proper length with accurate premeasurement & calculation. With these pipes glued into place and hanging where they should go, the fitting can be glued into place and will naturally be oriented in only one way. The difficulty with this idea is that the pipes all have play in them, so they need to be affixed to proper orientation as well as possible before doing this (that is, prevent the pipe & its attached fittings from rotating about the pipe's longitudinal axis.)

In my design, and I'd imagine most designs, the fittings all connect at standard orientations. That is, either in-line or at 45 or 90 degree angles to previous fittings. Unfortunately, the pipes between the fittings have no longitudinal reference lines, so you can't simply align two reference marks on the fittings to ensure they are at exact relative angles. The lack of these reference lines on the pipes seems like the most bone-headed missing feature of a manufactured product I've come across in construction so far. Unless these pipes tend to somewhat twist along their longitudinal axis after manufacture, then I see no reason why they don't paint/print one or more lines down the pipe for plumbers to use as a reference line.. That would be immensely useful. I'm considering securing the pipe on a flat surface and making my own reference marks at ends of the cut sections of pipe to orient fittings when gluing..

It would be easiest to just dry-fit everything into place, draw reference marks between pieces, then take it apart, glue together, and rejoin. In fact, many online references say to do this. Which is stupid. You can't dry-fit pieces of PVC together, they don't fully seat until you prime & glue them. That technique might work with other types of pipe that you can fully seat before welding together. And it could work with PVC if you only had a simple configuration with large tolerances.

This could be explained better with step-by-step pictures, but I'm trying to figure this out, and trying to get work done, not trying to teach you stuff! OK I'm going to go try this all out now..

Hopefully it will warm up!