Nibco built in seal

Hi all, I've been really trying to resist posting too much on here, but I feel like this question might save me a lot of time and trouble, so thank you in advance.

At the p-trap to drain tee connection in my tub, I used the nibco slip joint nut on this


1-1/2 in. PVC DWV Hub x SJ Trap Adapter-C48017HD112 - The Home Depot

Now I thought I confirmed that there is a built in gasket on that piece.

After installation, it's leaking from the top when under a tubs worth of water pressure.
I had to tweak the whole drain assembly a bit to get it to fit on the small tub.

I've loosened it and tried to massage the tailpiece into place better and retighten it but it still seems to leak.
Now I wonder if I should tear the whole drain assembly out and use a more appropriate piece at this joint or continue to fight to get the tailpiece straight enough to stop the leak.

Any advice? You guys have been a tremendous help.

 

Ok gave up on that whole thing and redid it with a regular zinc slip joint but and tapered washer cannibalized from the old tub because they don't have those at big box stores. Wtf?

Anyway, the nut was stripping on the p trap because it was so crooked, so I tightened the ptrap nut then muscled the drain shoe in place and barely wobbled the overflow up in place. I'll test it tomorrow, and if it leaks I'll throw my hands up and start crying. I understand why you just hire a pro to do this part, jeeeeeezes.