4 pumps in the nether, after a bit of time, can suck 25% of CPU.
According to debugger, when cleaning, Electripump causes a lot of lag by removing more and more flowing fluids. Removing them force a light update (laggy) and seems to propagate updates around it.
In game, you can see flowing fluid coming back almost instantly, like it was triggering by the 'cleaning' itself.
On the same idea, providing an option to limit the pump range would help reducing the lag.

This is with Mekanism-6.0.5.46.

Should be fixed for the next release.