Current Behavior:

For Dev who depends on create on modding, OpenEndedPipe$IEffectHandler is used for creating custom fluid leaking effect on Open Ended Pipe (or simply leaking point). However, when fluid has no corresponding BlockState, which means that fluid is a virtual fluid, FluidStack be passed into OpenEndedPipe$IEffectHandler#applyEffects has always 1 (mb) amount,

In OpenEndedPipe$OpenEndFluidHandler#fill, when FluidHelper.hasBlockState(containedFluidStack.getFluid()) returns false, passed-in value resource will be reset as same fluid with amout of 1(mb).

Example:

In our Create Addon Enchantment Industry, we add a virtual fluid called Liquid Experience, which obviously, represents experience. Player use various method to collect it form loots, experience nuggets and themselve's experience bar.
At leaking point, a reasonable behavior of liquid experience should be changing to experience orb that carries percisely leaking amount of experience. So we register corresponding IEffectHandler with following overrided OpenEndedPipe$IEffectHandler#applyEffects method:

    @Override
    public void applyEffects(OpenEndedPipe pipe, FluidStack fluid) {
        var players = pipe.getWorld().getEntitiesOfClass(Player.class, pipe.getAOE(), LivingEntity::isAlive);
        var level = pipe.getWorld();
        var pos = pipe.getOutputPos();
        var pipePos = pipe.getPos();
        var speed = new Vec3(pos.getX() - pipePos.getX(), pos.getY() - pipePos.getY(), pos.getZ() - pipePos.getZ()).scale(0.2);
        var xpPos = VecHelper.getCenterOf(pos);
        int amount = fluid.getAmount();
        if (players.isEmpty()) {
            awardExperienceOrDrop(null, level, xpPos, speed, amount);
        } else {
            int partial = amount / players.size();
            int left = amount % players.size();
            players.forEach(player -> {
                CeiAdvancements.A_SHOWER_EXPERIENCE.getTrigger().trigger((ServerPlayer) player);
                awardExperienceOrDrop(player, level, xpPos, speed, partial);
            });
            if (left != 0) {
                var lucky = players.get(level.random.nextInt(players.size()));
                awardExperienceOrDrop(lucky, level, xpPos, speed, left);
            }
        }
    }

In our expectation, we obtains leaking amount from passed-in FluidStack and distribute exactly same amount as obtained of experience to experience orb or nearby player.
Obviously we cannot see expected behavior since all passed-in FluidStack has amout of 1 (mb).

And there is neither javadoc nor percise explaination on wiki/Attaching-TileEntity-Behaviours. It definitely casuses confusing when user want to implement some amount-related-functions, well, with tons of time spending on debugging and making a patch by Mixin.

Possible Solution?

In order to keep consistency of old code and also provides a solution for situation which indeed needs that "amount", we can
add a new method into OpenEndedPipe$IEffectHandler:

		default boolean isAmountRelated(){
			return false;
		}

And make corresponding place in OpenEndedPipe$OpenEndFluidHandler#fill.