No, I am saying that the drain and trap do not meet code. We have those pesky things for a reason if nothing more than to confuse people. It would seem specious to ignore such things on a forum that primarily gives plumbing advice don't you think?
No common sense and this confusion you mention is why many DIYer type people don't follow codes but what is the reasons for this type Tee not being allowed, or installed correctly and a vent being required?
I see you added to the post I just replied to, here's a copy of what you added and my reply;
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Furthermore I do not believe that the 1 to 2lb difference in incoming pressure will have any effect at all on the equipment that Thinkup has selected and I believe that though perhaps not optimal, his equipment will perform to his satisfaction for many years.
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You had previously said in your first post in this thread that you have installed some water treatment equipment but you were no expert, or something very close to that.
Yet here you are disagreeing with me that to obtain full DLFC gpm flow in heavy filter mineral takes time and needs all the pressure it can get to successfully backwash it to total bed expansion and doing that ASAP is critical. So what do you base your opinion that 1-2 psi more will not make a difference on? Are you aware that full DLFC gpm and total bed expansion may not happen until the last couple minutes of the backwash cycle position run time?