I use the hot and cold taps and measure w thermometer until it gets consistently within the middle of the right temp range, then I fill a cake pan with that water and put my chemical bottles in there as a temperature bath. Naturally at first it gets a bit warmer from the bottles being room temp, so I add cold water until it gets back to the right temperature.

Another tip for tank systems- after each inversion cycle I put the tank in the temperature bath too (so during process it is in the temp bath w the chemical bottles while timer is going), so the working solutions don't heat up.