Air Tightness Difficulties

Hello everyone, My friend and I are moving on to trying to seal parts of the ship for spaceflight now that our production system works and have started hitting the problem of leaks we can't find. I recall being told there's a mod to make this much less difficult when I had this problem on my single-player world but never went for it... I figure it'd make things smoother on multiplayer but now I can't recall the mod's name.

Anyone know which mod that likely was?