this is not a native feature for mekanism 1.7.10 but we can add it

you can use the pressure gauge and right click on that bar to empty it, does the same with gases, doesnt make sense in this case but it what it is.

is the current ,method of emptying the tank on infusing factory satisfactory or do you still want to add a dump button?

It isn't needed, but would be nice to have, since the regular infuser has it