Sorry for the late reply.
But I think you need to set the Density inside.
FluidAttributes#createAttributes()
You can also change the colour and some other stuff there.
Edit: After some more looking, I saw that Density is already set to 1000, which means your Fluid has already density... I'll try to take some more looks
Seems like a Forge bug.
Durability seems to be the Attack damage.
TUTORIAL(1.7f, 5.0f, 25, Attack Damage / not durability at Tools, 3, ItemList.tutorial_item);
To overrun this go to your Registry / properties and add:
defaultMaxDamage(700)