Are upside down slip joint nuts okay?

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atatime

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Here's what someone recommended for a setup. I am discussing only the relevant parts.

There's a standard 1.5-inch horizontal PVC pipe under a kitchen sink. At the end of it, there's a 90* elbow with threads on each end. One end is attached to the horizontal pipe with a slip joint nut (and washer) by sliding it down the horizontal pipe and onto the threads. The other end of the 90* faces down toward the P trap. In this setup, a short piece of PVC pipe that's smooth on both ends (no threads) goes into the downward-facing side of the 90* and connects to it by sliding a slip joint nut up it and onto the threads on the downward-facing end of the 90*. That concerns me because the slip joint nut is upside down. Can you have an upside down slip joint nut like that and expect to have a water-tight seal? Thanks.
 

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slip joints work in all directions. The crappy translucent bevel washers are not very good. There are blue or orange bevel slip joint washers that work very well.
 
Here's the anatomy of a plumbing slip joint so you can see it seals at the bevel, so it works in either direction. And as breplum said, the translucent bevel washers are "crap".

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I'd go two 45's instead of two 90's

Unless there is something wrong with this setup, it's what works for me given my lack of experience (first time replumbing under a sink) and other issues that I can't delve into here.
 
No p-trap?
It's not the full setup. I showed that part because I needed to know if I could use and slip joint nut upside down like that. I'm sure there are better ways to do this job. But someone with some experience recommended it, and I understand it pretty well, which is important given my lack of experience.
 
Unless someone has an illustration of how to use two 45s and thinks that will be significantly better, I'm going to stick with this. I will dump the clear washers and get better ones. I'm connecting a pipe with a dishwasher extension between what you see and the P trap. That pipe has to go there because the dishwasher drain hose reaches only so far.
 
atatime, you really don't want to use an expandable flexible bellows fitting. They can be problematic. What you have it just fine like it its.
What problems have you had with the “ bellows fitting “ ?
 
just from the looks, seems like they would attract gunk / debris over time......moreso the more of an angle they were required to bend to ???? (me = NOT a pro, just a diy-er)
 
I don't know. But even if it does, it is still problematic and a poor choice for even the DIYer.
I think it’s a spin off of the “ radiator hose “ fix from back innthe good ole days.

I suppose it’s better than letting it drop into a 5 gal bucket and hauling it to the porch or dumping it down the tub. 🤣
 
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