When is it OK to run flat? (consecutive 90° bends)

On the 4" CI stack I'm installing, I've got a medium bend 90 (vertical to flat) that immediately transitions into a short 90, continuing its vertical plunge.

I'm supposing in that instance, there's no slope to concern myself with, as long as the two vertical sections are plumb.

Ok, so now reality: I've got a short 4" transition piece between these two 90s. I'm able to measure slope off of the outermost bands joining these three pieces together. The bands are 8" apart, so I should see 3/16" drop between them. Instead, they're dead level (measuring off of a laser line).

I'm trying to force the meager 3/16" slope, but am putting strain on the connections (which are snug but not fully torqued). I think it's because I've got good, square connections.

Should I loosen the bands and get my slope at the expense of a perfect connection, or should I run it flat for that short 4" knowing my two joints are seated perfectly?

Pappy always said " If it's going hard, you're probably doing something wrong"

Where is this "offset" Is it a wet stack or a dry stack?

Hi again Wally.

It's a wet stack, being fed by a single toilet directly above the medium sweep 90 (there's a Tee just above the 90 in the photo below).

You can see in the photo that I've got some shims wedged under the bend there, my feeble attempt to raise this end of the horizontal jog, and it's not being cooperative. The pipe is not connected above, i.e. free to move.

But now that I've had the night to think about it, I need to try loosening the couplers on the upper and lower ends of the 90s. I'm betting I torqued those down, expecting I wouldn't need to adjust them.

Imagine you are a drop of water coming down that stack. When you hit the first medium bend, are you REALLY going to be slowed down so much that you cannot make it to the drop off at the second bend, no matter how MUCH or how LITTLE slope there is in the intervening pipe. I don't think you have any problem.

I don't either, which is exactly why I'm asking the question. Although I suppose it's not so much the drop of water, but instead the poop and toilet paper that I'm more concerned with?!? I'm having trouble accepting that this minimal 1.2° slope can have such an effect over such a short distance, especially with a pressure-flush toilet being my source of, er, um, "soil."

Soooooo... just let it be? 'cause I'm ready to make my final connection to the vent pipe through the roof.

BTW (sort of off topic), my plumbing supply shop has twice expressed concern that I've been buying the 4-band "heavy duty" connections for $9, when they have the $1.70 two-band couplings that I've been using only on my dry connections. But everywhere I look (here at the house from the plumber before me, at work, at the grocery store) I almost exclusively see 4-band. Is there a big performance difference?

I do not think I have used more than a half dozen, and maybe not even that many, four band couplings in the past 40 years. Before that I had used exactly ZERO bands of any type.

Lol! Yeah, so I probably paid out $100 more than I needed to. Well, I can't say I would have done any differently if I were buying again today (I'm all for overkill when it comes to leaky drain pipes). But still, good to know...

Did a little bit of digging re: the heavy duty couplers and found some info, makes sense that the extra material is what was giving me a hard time shifting this section of pipe to the right orientation. Got it all squared away now; I figure all I needed was a trivial 0.3° of bend per connection x 4 adapters which shouldn't have been any problem. With this crooked old house, maybe it's prudent I installed 4-band. Still can't figure out why they cost as much as they do! As usual, thanks fellas for your input.

http://missionrubber.com/Products/HeavyWeightCouplings.php

and

http://www.fernco.com/files/literature/shielded_couplings/NoHub_300.pdf

quote; Still can't figure out why they cost as much as they do!

It is because they probably make a hundred two band ones for every single four band coupling. Therefore is the economy of scale. If you want a manufacturer to make you ONE special bathtub, it will cost a lot more PER TUB, than if you wanted 1,000 of them.