The idea is to taxi or warm up on one tank (least full) then change tanks to (most full) then do the run up then toff on the (most full) tank that you have just tested.
Then both tanks are tested and you have not interfered with the fuel selector directly before take off.
And no I have not consulted any checklist/poh it is a procedure that is quite common, last plane I used to use it in was the Beaver when only using the front and centre tank.