Pipe and Fittings ?

I will compare 4 inch pipes for discussion purposes and use this for my question(s).
There appears to be three types of 4 inch pipe as follows:

ASTM...................OD.................Wall Thickness................Other

2665 .................4.50......................... .237 ....................... Schedule 40
3034..................4.215....................... .120 ........................SDR35 (also called sewer pipe)
2729..................4.215....................... .075 ....................... Thin Wall

To confuse matters even more manufacturers now have (within PVC and ABS) pipes designated as
Cellular Core, Foam Core, and those made with Recycled material. OD and wall thickness
appears to be the same as the above listing.

Questions:

1) I have found fittings for Schedule 40 and Thin Wall but NOT for SDR35. Is there a separate series of fittings
--- or -- do you use the same fittings as the Thin Wall for SDR35 since pipe OD is the same?
2) Is the primary difference between Schedule 40 and SDR35 the fact that Schedule 40 can be put under pressure
even though it may also be designated as DWV?
3) Where does ASTM 2759 fit into this picture?

SDR is a replacement installation waiting to happen. In other words it is "junk". Anything thinner would be absolutely worthless even though you would use SDR fittings with it. The big "difference" between SDR and sch40. is that sch 40 will not collapse when it is buried. SDR WILL collapse, crack, flatten out, etc. from the weight of the dirt., and you should NOT use it inside a building for a drainage system. Only use it where you can get to it with a backhoe to dig it up. THe other factor is that the I.D. of the pipes SHOULD be equal for interconnection purposes which is why SDR has a 4" i.d. but a smaller o.d. because of the thinner wall. "Thin wall" pipe would create a ridge at EVERY Fitting because its i.d. will be greater than 4".

hj: For me, a lot of this pipe stuff is confusing -- to many options.
From what I understand, SDR is a calculation (Pipe Wall / Pipe Diameter) and can apply to any pipe -- even pressure rated.
SDR35 is different than what is called "Thin Wall". SDR35 lies between Sch40 and "Thin Wall"
What I've found is that even though I wanted to use Sch40 for a septic redo, The D-Box and Tank Gaskets seem to only take SDR35 NOT Sch40.
So this seems to force you into SDR35 whether you want it or NOT. AZ state regs call out SDR35 or better -- yet if the gasket will only take SDR35 -- there is NO "or better"

Been working on the following -- will update as I get more info. The one "Key" piece on info missing is Max Burial Depth. In talking with one of the pipe manufacturers
there is no rating -- at least that they will provide -- of crush depth.

I've seen the smaller diameter PVC used for shallow outdoor sewer runs, in conjunction with gasketed fittings. From a distance, it seemed to be heavier-walled than 1/8-inch, especially since the ends were beveled to work with the gasketed fittings. Material like that would fit the wording "better than SDR-35" on account of SDR-35 being a ratio of pipe diameter to wall thickness, and a 'better' pipe would have the same outside diameter, but a smaller SDR number, on account of having thicker pipe walls.

My own personal use of the ASTM 3034 PVC has only been the fittings, used for downspout connections and corrugated drain pipe, as representing an upgrade over the home-center thinwall pipe and fittings made of styrene.

The o.d. of SDR is calculated by having a true 4" i.d., the same as sch. 40, and then adding twice the wall thickness. To use sch. 40 with your devices, you glue an SDR x sch. 40 bushing on to the SDR.