Necessity is the mother of invention.
Several letters have mentioned the problem of temperature control especially using powder developers As the getting the temperature adjusted is harder than using a one shot diluted developer. I use one shot developers exclusively myself ,. However the fix and wash still have to be adjusted too. Over the years I have cobbled together several pieces of odds and ends to serve that purpose, which also works for undiluted developers.. I store my fix in the standard quart plastic bottles. They will fit in either an old 4 lb coffee can or in my case, a stainless steel flour container that lost it’s lid. Hot running water in the can bring the temperature up very quickly. To lower the temperature the working solution developer is placed in my four reel stainless steel developing tank and cold water from a hose played on the side of the tank . Or the large coffee can filled with water and some ice cubes. A large clear plastics container made to store shoes in is my temperature control. It is also the tempered water I will use for washing the film, using the Ilford method of wash and dump And it conserves water I use 3 gallons total ..Since my summer water temperature is usually 72 degrees I base my developing times on that. If I need it cooler I put some ice cubes in the bath until the proper temperature is reached and then remove them. Plastic for all of its fault is very good about holding temperature fairly steady.
The actual tank (I use stainless steel tanks) with film sits in a tray of the same tempered water
I use the same techniques when I do sheet film in an 8x10 Unicolor drum with equally good results. The drum it self holds temperature steady as well. I have found that if all the solutions drift equally, usually downwards , there is little danger of damage to the film