How to Reduce Multicolor Purge Waste: The Settings That Actually Work

Your AMS, CFS, ACE Pro or CANVAS isn't broken. It's flushing on cautious factory defaults. Here's how to shrink the pile on the printer you already own, ranked by what each fix saves and what it can cost you in color bleed.

By Dreaming3D in Carmel Valley, San Diego. Updated September 27, 2026. About 11 minutes to read.

First, you have three piles, not one

Every single-nozzle multicolor system works the same way: several spools, one hotend. When the color changes, the old filament left below the cutter has to be pushed out before the new color prints clean. We covered the physics in our H2C piece. What trips people up is that the slicer's waste number is really three separate things, and each one has a different fix.

That third pile matters when you read marketing. When a new printer claims "zero grams" of purge, check whether it's just moving the flush into infill. That's exactly what we found in Creality's SparkX i8 footnotes, and it's a setting Bambu Studio and OrcaSlicer already have.

The fixes, biggest payoff first

This list is ranked by what each fix saves against what it risks. The first two don't change how much the printer flushes, so they can't cause color bleed. The middle ones trade some safety margin for grams, so they need a test print. The last one costs money.

1Batch copies on one plate

Polymaker's wiki explains the logic well: when several objects share a plate, the color changes happen at the same time for all of them, so each extra copy adds almost no flush. Four keychains printed together cost roughly one keychain's worth of purge. Four separate jobs cost four.

If you sell small multicolor parts, this is the setting that decides your margin. Fill the plate before you touch anything else.

2Flush into infill, support, or a spare object

Bambu Studio can send part of each flush into places nobody will see: the model's sparse infill, its support structures, or an object you mark as a purge target (in object settings). OrcaSlicer, ElegooSlicer and Anycubic Slicer Next are all built on the same slicer family and have similar options.

Three catches. In Bambu Studio, all three options do nothing unless the prime tower is enabled. Bambu's wiki warns against flush into infill with transparent filament, because the mixed colors show through. And infill can only hold so much, so small or thin-walled parts barely benefit.

A purge object works best when you'd print the part anyway and don't care about its color, like internal gears, a jig or test coupons. Flush into support is almost free, since you're going to throw the supports away.

3Calibrate, then lower the flushing volumes

Every one of these slicers keeps a from/to table of flush amounts in cubic millimeters, plus a global multiplier. The auto values come from your color swatches. Dark to light gets a large flush, light to dark a small one. Bambu's wiki says the defaults lean high to protect print quality, and suggests 0.8 or 0.9 as a quick way to save filament, provided you test first.

Owners go further. On Bambu's forum, people report running 0.5 to 0.6 with auto-calculated values, and one owner who calibrated no-name PETG found he needed only about 43% of the amount Bambu Studio estimated. Those are their colors and their filament, though, so use them as a reason to test, not as a number to copy.

Where this goes wrong. The auto calculation only sees the swatch color, not how strong the pigment is. The pairs that bleed are predictable: anything into white, anything into clear or natural, and black or red into a light color. Raise those specific cells instead of inflating the whole table. Also leave material changes alone. Bambu Studio 2.08 deliberately raises the flush between PLA and PETG to protect layer adhesion.

The calibration takes under an hour. The steps are further down.

4Turn on "Long retraction when cut" (Bambu)

This started as a community G-code mod by Leon Fisher-Skipper. It pulls the filament back before the AMS cuts it, so less old color is left in the hotend to flush out. Bambu adopted it and announced it in April 2024 as saving up to 25% of purge volume. Bambu's release notes put the saving at about 2.4 × the retraction length in mm³, so an 18 mm retraction saves about 43 mm³ per change.

It's still labeled experimental. You turn it on in each filament's setting overrides, one filament at a time. Leon's page says Bambu's own tests showed problems with silk PLA and Bambu's support material, so leave it off for those. After you enable it, recalculate flushing volumes, because the saving comes out of the flush table.

5Design for fewer color changes

A flush costs the same whether the new color covers a whole face or a single dot. Elegoo's own FAQ gives the same advice we would: merge areas of the same color, cut color changes that don't add anything, and question whether small decorative details need to be multicolor at all.

• Change color by height. A sign with a base, a body and top lettering needs two changes in total. Color that alternates on every layer needs hundreds.
• Print color-separated parts and assemble them. Parts that snap or glue together never need a flush.
• Count before you slice. The slicer preview shows the number of filament changes. If a tiny accent adds 200 changes, it's worth a second look.

6Shrink the prime tower last

Once your flushes are clean, you can make the tower narrower and lower its prime volume. Don't delete it on your first multicolor print. Without it you lose the flush-into options in Bambu Studio, and you risk blobs or weak first lines right after each change.

7If it still bothers you, it's a hardware question

Settings can only shrink the waste from a single nozzle. Machines that give each material its own nozzle, like IDEX printers, tool changers and Bambu's Vortek system, avoid most of the flush entirely, but they cost far more. We've covered the H2C and Sovol's M1D. Even those still prime and wipe, so "near zero" doesn't mean zero.

The math on one job

Here's the worked example behind the chart at the top. It's a four-color part with 240 filament changes and an average auto flush of 350 mm³ at a multiplier of 1.0. That average is an assumption within the range that published auto-calculated tables show. PLA weighs 1.24 g/cm³, so each 1,000 mm³ flushed is 1.24 g of plastic. Each row keeps all the fixes above it.

Two things stand out. The risk-free fix, batching four copies, saves almost as much as all the tuning above it combined. And on a single part, the full 104 g is only about $2.08 of filament. The part that really hurts is time, because every flush is extrusion the printer does instead of printing your part. That's what batching and fewer color changes buy back.

Assumptions: a tested multiplier of 0.70, an 18 mm long retraction, 6 g of flush absorbed by each copy's infill, and color changes halved by redesign. We left the prime tower out. Your printer's numbers will differ, so the slicer's own "flushed" figure is the one to watch.

Where the settings live, by brand

If your machine won't take a multicolor job at all, or it jams mid-swap, that's a feeding problem rather than a flushing one. Start with our AMS troubleshooting guide. Damp filament also makes feeding and oozing worse, which matters in coastal San Diego. Our dryer guide covers what actually removes the moisture.

How to calibrate flushing volumes in about 45 minutes

This works on any of the systems above. You'll need a kitchen scale for the last step.

1. Sync your spools and recalculate

   Load the exact filaments you'll print with, sync the slicer to your AMS, CFS, ACE Pro or CANVAS, and make sure each slot's color swatch matches the real spool. Then hit the recalculate or auto button in the flushing-volumes dialog. The auto values are only as good as the swatches they're computed from.

2. Print a flush calibration model

   Print a purge calibration model for your system: community models such as the AMS Purge Calibration on MakerWorld (Bambu) or the CFS Purge Calibration Test on Creality Cloud print strips at stepped flush amounts so you can see where each color change comes out clean.

3. Read the worst pairs first

   Find the lowest flush where the new color prints clean. Check the hard transitions first: anything into white, anything into clear or natural, and black or red into a light color. Those set your floor.

4. Enter per-pair values or one tested multiplier

   Either type the passing values into the individual from/to cells, or drop the global multiplier to the lowest value your worst pair survived. Raising two bad cells is better than inflating the whole table to protect them.

5. Turn on the Bambu retraction and flush-into options

   On Bambu printers, enable “Long retraction when cut (experimental)” in each filament's setting overrides, then enable flush into infill and flush into support. Leave the prime tower on, because Bambu Studio ignores the flush-into options without it. Skip flush into infill for clear filament.

6. Weigh a real print

   Run a real job, collect the purge from a known number of changes, and weigh it on a kitchen scale. If it's far heavier than the slicer's flushed-grams estimate, the printer isn't doing what the slicer planned, and that's worth a firmware check or a support ticket.

7. Save the project as a template

   Save the tuned project and start new prints from it. Bambu Studio users have reported that re-syncing the AMS recalculates the table, so check your values after every sync.

What this means for San Diego makers

Factory defaults are the right place to start, since they're tuned not to bleed. But if you're selling multicolor parts at a craft fair in North Park or turning out club keychains, batching and a calibrated flush table are the difference between a print that pays and one that doesn't. The flush time also runs the printer longer, and that shows up on your SDG&E bill.

We run multicolor FDM jobs from $7/hr of machine time plus material. If you'd rather have the parts than tune the machine, send us the file. What we don't print: metal, flight hardware, firearm components, load-bearing or safety-critical parts, and patient-contact medical devices.

Frequently asked questions

Keep reading

• Best Budget Multicolor 3D Printers Under $500Five multi-filament machines that won't wreck the wallet.
• The Bambu Lab H2C and the End of the Purge TowerHow swapping hotends instead of flushing cuts the pile.
• How to Fix Your Bambu Lab AMSJams, feed errors and the usual culprits.
• Creality vs. Bambu Lab: Which Is the Best 3D Printer for 2026?CFS against AMS, and which brand fits you.

Your turn: what's the lowest multiplier your worst color pair survived, and on what printer? Tell us on Instagram at @dreaming3dprinting and we'll add the best results to the next update.

Sources

1. Bambu Lab Wiki: Reduce waste during filament change
2. Bambu Studio 1.9.0 Public Beta 2 release notes (long retraction ≈ 2.4 × length mm³)
3. Bambu Lab on X, April 2024: “Long retraction when cut” announcement
4. Leon Fisher-Skipper, “Reduce purge by up to 45%” (MakerWorld)
5. Bambu Studio 2.08 release notes (material-aware flushing)
6. Bambu Studio issue #3821: flush table recalculates on AMS sync
7. Creality Wiki: Flush Volume Setup Guide (Creality Print 6)
8. Printables: Creality K2 CFS Flush Calibration, owner comments
9. Anycubic Wiki: Reduce waste during multi-color printing
10. Anycubic Wiki: Kobra S1 firmware update guide
11. Elegoo Wiki: Centauri Carbon 2 Combo FAQ
12. Fabbaloo: Hands on with the Elegoo CANVAS upgrade, part 3
13. Polymaker Wiki: Reduce Purge Waste
14. Bambu Lab Forum: AMS flushing volumes calibration and purge reduction
15. Bambu Lab Forum: Making better use of flush-into object in Bambu Studio

Tags: multicolor 3D printing, purge waste, flushing volumes, Bambu Studio, OrcaSlicer, AMS, CFS, ACE Pro, CANVAS, prime tower, 3D printing tips, San Diego 3D printing