Small amount is better than no amount.
And, of course it varies with the temp/condition of the snow, but the general rule of thumb is 10" snow - 1" H2O
so, if you have a 5qt crock pot (approx. 4,800 ccs, or 160 oz) you should get about 480 cc or 16 oz of water.
so, load up that crock pot tonight, when you get up n am, pour melted snow (now H2O) into a container, and load'er up again!
You know, kind of like the shampoo bottle instructions = lather, rinse, repeat...

For 1 gal. flush, you will only need to do that

8 times is all. Not too bad!