I’ve been doing a bit of research into pressure frying and I’m curious to hear if anyone has thoughts on why commercial pressure fryers do not typically exceed 12-15 PSI. According to Henny Penny’s literature, their pressure fryers operate at 12 PSI with an oil temperature of 325 F. At 12 PSI, the boiling point of water is roughly 245 F so there’s an 80 F difference between the oil temperature and water boiling point. Even at this relatively low temperature, pressure fried chicken is roughly 30% faster than atmospheric fried chicken. Wouldn’t we be able to fry chicken even faster if the pressure and temperatures were increased? Why do you think 12 PSI is industry standard? An extreme example would be oil temperature at 450 F and pressure of 155 PSI. This would yield a boiling point of 370 F and would maintain the 80 F differential between oil and boiling point. This would likely require extra thin pieces of chicken to fully cook before the breading burnt, but I’d imagine there’s a point somewhere between 12 PSI and 155 PSI that would allow for much faster frying times without burning the breading. 
The key thing is that you empty and wash the container regularly (ideally daily, but at least every few days). If there is a bad smell that is a sign that something is wrong; most likely some milk remained somewhere like a screw top or drops on the lid, which has gone off in some way. Any bottle sold for drinking water should be food safe in terms of its material, so I would be very surprised if you cannot find anything. However, I would try to find a bottle which:  is easy to clean completely, so no complicated closing mechanism or built-in drinking straw. will provide reasonable insulation while the bottle is out of the fridge, for example a thermos bottle (which uses vacuum in the walls to insulate the contents).  Anything suitable for carrying hot coffee is likely to work well for your needs, in case that's a useful way to search. 