Karen use both i would suggest run the six inch with about 2 incheses in it as the main boilingl pan. Use thr 4 incj as a earming pan anf laddel hot sap to the 6 inch . Laddel it over just enough not to loose the boil
Before you know it you will be outta sap.. What you temove from 4 inch for the
6 inch replace with fresh sap

