How much salt?

[Gardner Yeaw]

I am now planning several trips through December in the North East.
Randy and others suggested rock salt in the grey and black tanks to
prevent freezing. When I was planning one trip I thought pink stuff
would do, but now with multiple trips I need a better solution.
Getting rock salt into the black tank is simple, but the grey tank is
another matter. I will need to disolve it in containers of water and
pour it down the drain in the shower or kitchen sink. So how much do
I need to use? I looked up some calculations on the internet, but
they went into molels or some other unGodly scientific terms. All I
want to know is how many pounds of rock salt to protect down to 20
degrees? (60 gallons max)

Gardner
78FC33 (streching the season and loving it)