Allow flush-into-object to fully replace the prime tower

Is there an existing issue for this feature request?

• I have searched the existing issues

Is your feature request related to a problem?

Currently, enabling "flush into object's infill" still requires the prime tower to remain active. This makes the feature far less useful than it could be, especially in cases where the prime tower itself generates significant waste that offsets or eliminates the savings from object flushing.

On a recent 3-filament print, my slicing result showed:

Purged: 16.59g (5.53m) Tower: 10.71g (3.55m) Total waste filament: 27.3g on a single print

If flush-into-object could fully replace the prime tower, that 10.71g of tower waste could become zero being absorbed into the infill of objects that would have been printed anyway.

Which printers will be beneficial to this feature?

All

Describe the solution you'd like

The solution I'm proposing is to add an option to fully disable the prime tower while keeping flush-into-object enabled. The slicer already knows two things:

The required flush volume per filament transition (from the flush matrix) The available infill volume per layer per object

These two numbers are enough to route purge volume intelligently. If object infill can absorb some or all of the required purge volume, that amount should be flushed into the object first. Any remaining purge volume that cannot be absorbed by available infill would then fall back to a traditional poop/purge rather than requiring a prime tower.

Additionally, allow users to designate a specific object as the primary purge target, so its infill is prioritized for absorbing transitions. A sacrificial object placed on the build plate specifically for this purpose (a simple cube, a spare part, a Gridfinity bin) would give users full control over where purge filament ends up while reducing or eliminating the dedicated tower entirely.

Describe alternatives you've considered

1. Manually increasing infill percentage to create more absorption capacity. This works to reduce poop but wastes filament in a different way and still requires the prime tower to be present.
2. Disabling the prime tower entirely without object flushing. All of the purge is pooped but could have been used in objects infill or sacrificial purge objects like the spare parts or gridfinity bin mentioned earlier.
3. Accepting the tower as unavoidable. This results in significant cumulative waste across multi-color prints. Often to the point that the purge tower eats up any potential savings of letting the purge go into the objects infill or a sacrificial purge object.

Additional context

The prime tower is fundamentally a workaround for cases where no better purge target exists. For users already printing objects with infill, the tower is redundant if the slicer can route purge volume into that infill instead. The flush-into-object infrastructure already exists in OrcaSlicer. This request asks that it be elevated from a supplemental option to a capable replacement for the prime tower when the user chooses to enable it. The two key data points the slicer needs to make this work are already being calculated -- this feels like it could be a relatively contained change with meaningful real-world impact on filament waste across every multi-color print.