So... this works.
event.custom({
"type": "thermal:bottler",
"ingredients": [
{"item": "minecraft:glass_bottle"},
{
"fluid": "create:potion",
"amount": 250,
"nbt": {"Potion": "minecraft:strong_leaping", "Bottle": "REGULAR"}
}
],
"result": [{"item": "minecraft:rotten_flesh"}]
})
However, it seems I cannot replace fluid with tag. I would like to define this with the minecraft:potion tag so that I do not need separate recipes for create:potion, tconstruct:potion, immersiveengineering:potion and so forth. Is this possible? And how would I determine if something like this is possible, in general? That way I don't have to ask for all kinds of recipe types, because I have come across similar things before where I would like to define an accepted fluid, but can only seem to use a tag for example.