There is a pyro taunt that was not added to the game and was removed from the animation files, it's called pyro_sit.
This mod replaces Taunt: Pool Party with pyro_sit.
Good things about this mod:**
It behaves the same as Pool Party! It will take a second for Pyro to "snap out of his daydream" when you want to stand back up (This is because it needs to fit the length of the Pool Party Taunt).
Pyro occasionally takes a deep breath while sitting.
Replaced the sound of the Pool Party because it simply doesn't fit with Pyro sitting.
The whole pyro_sit animation is there! I somehow had the whole animation before it was removed from the game files so yay.
I smoothed the animations slightly.
Bad things about this mod:
Does not work in sv_pure... duh.
Due to the unavoidable nature of modding sound files, some sounds in the game share the same sound clips as the Pool Party Taunt so they will unintentionally not play. It's nothing noticeable though, you would not hear a splash when you jump into water for example. You also wont hear the "extinguishing" sound for when you have extinguished an ally.
You need to own Taunt: Pool Party in order to fully use this mod.
Apart from those 3 things, that should be all the bad stuff.
If you want to use this with other taunt replacement mods, you must know how to extract .vpk files and replace some _animations.mdl files to their correct directories, www.google.com is a good way to learn how.