1990 SeaRay 350 Express Cruiser - Winterizing / Draining My Fresh Water Tank

Hello Folks - First time winterizing this boat as previous owners stored in an indoor heated facility. 70 gallon fresh water tank. Ran all outlets and drained to the 3" height mark, before outlets sputtering occurred, on a tank measuring L80" x W24" x H13". Doing the math leaves me with approximately 16 gallons in a 70 gallon tank. I have read all the previous info / posts info hand in hand with this topic and other than jumping through hoops to completely drain the tank, it is what it is.
The question being, can anyone approximate / recommend how may gallons of -50 degree celsius / - 60 degree fahrenheit anti-freeze I should add to prepare for maximum lowest winter temperatures of -10 degree celsius / + 14 degree fahrenheit? I ask because what I do pour in will get somewhat / considerably diluted by the freshwater left in the tank.

Thanks - Craig

I think you should drain completely and maybe blow out lines through the dock water connection. Dump maybe a gallon in tank and use the line before pump to suck anti freeze through system until pink at all faucets. Bypass water heater as well. This would need maybe three gallons tops

Completed the job this morning and here is what Thanks I did: I cut the hose from the tank 12" before the input into the pump and installed a t fitting whereas I switch one way to pull from the tank to utilize as normal and also drain the majority of the water from the tank when winterizing. Then I attached a separate 18" input hose to the other t portion where I can switch to pull directly from antifreeze jugs to winterize all the fresh water lines (galley, head and rear washdown tap), without having to pull from the tank. All done, utilizing less than 3 jugs. As to the water left in the tank, I will treat and flush the whole system in the spring several times to bring all up to potable / drinkable.

Dump some cheap vodka in tank and you’ll be fine

Almightys said:

Dump some cheap vodka in tank and you’ll be fine

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Vodka in Canada, even the cheapest, is expensive compared to the US - $22 US for a 26 ounce bottle is the cheapest! A 60 ouncer is $48 US ....

Craig Lescombe said:

Vodka in Canada, even the cheapest, is expensive compared to the US - $22 US for a 26 ounce bottle is the cheapest! A 60 ouncer is $48 US ....

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Wow that’s crazy. You can get a 1.75 liter bottle here if the cheap stuff for $11 USD. horrible stuff to drink which may induce blindness or coma but great for the tank lol