I have the etchant (ferric chloride) in a small plastic container that I put in an old washing up bowl with about 1" of very hot water in it. Etching takes about 5 minutes with constant agitation.
I agree with Leon. I have a bubble-etch tank with heater, but I never use it. Partly because it takes a fair amount of solution, which wastes etchant for small boards (since it has a limited life). Also, I find the bubbles aren’t actually very effective, since they tend to “stick” to the PCB surface.
I just use ammonium persuphate in a small plastic tub, heated in a pan of hot water. Etching only takes a few minutes when you keep rocking the tub.
If I was making lots of PCBs regularly I’d probably make a “spray etching” tank, which is similar to what the commercial places use.
Like you, I bought a bubble-etch tank a couple of years ago, tried it once, and went back to my usual method. It took ages to heat up, and etching was slow and uneven.
Back when I was etching boards all of the time at home, I used a fairly large Tupperware container for holding my FCA. I would nuke it a bit in the microwave to heat it BEFORE putting the board in the FCA. The heat and agitation really sped up the process to about 5-10 minutes, depending on the size of the board.