I don't have a dump for you because the process ended itself without a bug report
So, take this below:
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This is a L connector. When put in place the first time (Dropped where it connects the two pipes), the game works ok. When you rotate it once, the game works ok. Rotate it twice more and you get to this position above. Rotate it again and the game crashes so hard it doesn't even bug splat.
What it seems to be is, if pipe 1 is connected to pipe 2 via an underground connection, and you rotate pipe 1 into any position where another underground connection from pipe 1 will immediately take it's place pointed at pipe 2, the game crashes.
1.) Open the save attached to this post using the mod underground-pipe-pack from the original post.
2.) just above the start point to the left or somewhere near the spawn point should be the L bend pipe and the four way pipe already pre-made. Just rotate either one to test and narrow down the bug I speak of here.
This happens with the underground L, T, and X connectors.
I've tested the rest of everything such as the four to four pipe, and made this concoction:
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That's 8 fluid box connections. That works great.
Also, I greatly appreciate making pumps and pipes (and really all fluid boxes) show their underground connections if they have them. That's amazing and I always wanted it.