The XP tap works with any fluid that is tagged EXPERIENCE, however some mods have other ways to convert experience into/from their fluid, and if it doesn't match Mob Grinding Util's values it will result in either infinite XP or disappearing XP.

I am asking for a way, for either mod pack makers or other mod developers, to configure the amount of fluid per XP orb for specific XP fluids.

which mod has a problematic conversion rate?
all mods i know of with liquid xp fluids use 1xp / 20mb

what is their xp drain called? im poking around in the source and have not found it yet.

Create Enchantment Industry
https://www.curseforge.com/minecraft/mc-mods/create-enchantment-industry

If you do a "loop" with their XP drain and Mob Grinding Util's XP tap you loose XP.

It's the "disenchanter" it also absorbs the XP of any player standing on it

Here is the relevant part https://github.com/DragonsPlusMinecraft/CreateEnchantmentIndustry/blob/483394f8fca730edecf990b83a23d2989515013a/src/main/java/plus/dragons/createenchantmentindustry/content/contraptions/enchanting/disenchanter/DisenchanterBlockEntity.java#L208

It seems to use 1xp value as 1mb, if this line takes mbs as input (I don't know) https://github.com/DragonsPlusMinecraft/CreateEnchantmentIndustry/blob/483394f8fca730edecf990b83a23d2989515013a/src/main/java/plus/dragons/createenchantmentindustry/content/contraptions/enchanting/disenchanter/DisenchanterBlockEntity.java#L222

What modpack is this in?
CreateEnchantmentIndustry does not tag its fluid as experience, so someone else is tagging it.

I was using this modpack https://www.curseforge.com/minecraft/modpacks/ragnamod-vii