So, I noticed this item has the L facing a specific direction. Though there is a one in four chance it is the one you need, given that rotating the item rotates both the L configuration and the aboveground connector.

I don't see any solution other than making three additional items for the mod. Is this correct?

Did you rotate the underground portion by pressing CONTROL+R?

You'll always only be able to make that specific corner, and always receive it when mining. As per the description it is so that you don't hold 19 different items when there's only 9 pipes. I may need to fix this in the future due to the blueprint issue.

Been thinking on this, and I think what would be more useful than that specific L corner would be a two-way straight through segment with a surface pipe that points perpendicular to it. Kind of like how you've got one now where the surface pipe goes parallel to it. We've already got L junctions which are sufficient for cornering. But I'd totally use a perpendicular one because a lot of times you want to join together a series of chemical plants right at the input or output, but I've been using the T junction for this. And those can accidentally connect to something unintended.

There's L and I connectors for singular pipe to ground. I haven't expanded into specialised multiport to ground yet. I do have a pipe that has a four way underground in the mod.

The pipe behaves like a normal pipe would, (up to four directions on the surface) and has the 4 way underground up to 10 or 11. I think it was 11

Hmm I must have failed to explain what I was saying.

https://i.imgur.com/oiPn7I1.png
If you look at this image, what is circled in RED has two paths for fluid to go. What I am suggesting is a pipe just like this but rotated 90 degrees. And then you can get rid of the one which is crossed out in red because that is a mostly useless pipe.

At the moment, I am using the one circled in BLUE to put on a row of chem plants. But it would be better to connect them with one like the red circled item rotated 90 degrees.

You can rotate the underground part of pipes by using CONTROL+R.

The L connector can face all four directions, just as the perpendicular can go E-W/N-S

Oooh very cool! I missed the thing with CTRL-R. Thanks.
When you first mentioned it, I thought you were talking about normal rotating.

No problem.