I think you asked about how much you should sparge with?

I think the best way to figure it out is to start with the volume you aim to collect in your FV, and add in all your losses along the way to get the total water required, subtract your mash volume and what is left is your sparge volume

Let’s say you want 20L in your FV. You might lose 2L in evaporation, so that’s 22L.

Depending on your system you might have some dead space in your mash tun and boiler, say 0.5L each so that’s 23L

grain is reckoned to absorb 1L/kg so for 4kg (say) of grain we lose 4L, so that’s 27L needed.

a “standard” mash is 2.5L per kilo of grain so we need 10L for the mash, and the remainder is used for sparging (17L).

Your own losses will be different but that’s how I worked it out before I had a brewmaster

– Stuart (Oz) Osgood