I didn't follow your advice on that, since washing soda isn't so abundant here. I usually heat baking soda (sodium hydrogen carbonate) instead, but now I went in another route and tried HC-110 in order to avoid the fog. Well, it was a failure, since it didn't get the density right at first developer and the second dev just coloured all of the film in black.Dimitar, I would suggest you use before the b&w develator a prebath - sodium carbonate 20 g / l. Time = 3 min. at room temperature.
My next attempt was to use LITH developer as a first dev and utilize it's insane contrast. Unfortunately my LITH is a local brew, unmarked, so if anyone wants to try it, my starting times will be useless.
So, in the LITH dilution destined for paper, I souped ORWO UT-18 (shot as 12ASA in the shadows) for 6 minutes at 20 deg. The contrast of the negative, needless to say, was insane, but probably my second dev. (diluted RA-4 for 5 minutes) was insufficient, and the final slide is really low in density. See the attached images. The crane was bright orange against a blue sky.