[Brian C. Miller]

Coca-Cola can make a leak proof bottle for about 2 cents. So can multitudes of other manufacturers. Why cannot there be a film tank that absolutely, really and truly does not leak even one drop?

And one that holds temperature like a Thermos?

Let's see:
Stainless steel tanks with steel lid: leaks. Why? No gasket. Not much, but it does. No big deal.
Stainless steel tank with rubber lid: No leak.
Patterson tank, plastic/rubber lid: No leak.
Jobo tanks, using plastic/rubber lid: No leak.
Jobo tanks, using cog lids: No leaks when attached to lift unit.

Heat:
Tanks go into tempered water bath. No problems.

If you want to develop your film in a Coca-Cola bottle, remember to keep the lights off. If you want to develop your film in an insulated jug, which is just fine IMHO, you'll need to switch off the lights when changing chemicals.

And remember, the Combiplan is far superior to the Yankee tank, which isn't sealable at all.