Have no idea about volume but in changing ours we disconnected the heater hoses at the front "radiator" and blew them out (1+ gal). We "flushed" 4 times until only clean water came out. Suggest at least one gal. of 100% Final Charge (hard to find) so that any residual clear water will not dilute the mixture to less than the 50/50 premix. Book says 40 to 60% mix is OK BUT............
WalMart had a 15 gallon metal wash tub for $9.00 - Volume was pretty easy to figure as "volume out = volume in". The tub is now used for oil changes
Hal & Ginny Miller '04 Beaver Santiam PRT40
'04 Saturn Vue - US Gear Brake - Blue Ox tow
3"girls" (2 Irish Setters - 1 Retriever) - RIP Annie & Emily (12/26/2017)