Sloshing shouldn’t really lag, especially with a Distillation Tower that typically only runs until one of the Output Tanks is full. Also the sheer presence of Covers on a Pipe is more laggy than the Fluid distribution, since once any Cover is on it, it has to check if there is Covers on any particular Side or not, and if there is, it has to ask the Cover if it is allowed to go that way, at which point just moving the Fluid is easier than asking the Cover before moving it.
I wonder why people even bring up Lag with my GT6 Fluid Pipes considering it is absolutely impossible to even measure that Lag with anything. Opis sure as heck cant measure it, and neither can any other of those Lagfinder Tools, because the Pipes tick outside of ‘updateEntity()’, in order to ensure even distribution. You would need to use jvisualvm and at that point most people cant figure out how that even works.