TL;DR
Cleaning a dryer drum is a three-part job: identify what the residue is, remove it with the gentlest thing that works, then run a sacrificial load of old damp rags to prove nothing transfers. Never spray a flammable solvent into a dryer, and never run the machine with solvent still wet inside it.
First, what is on the drum?
The removal method depends entirely on the material, and guessing wastes effort.
Waxy and colored streaks usually mean a crayon, a lip balm or a lipstick went through. Wax melts, smears around the drum, and re-deposits on the next load.
Sticky dark smears point at chewing gum, adhesive from a sticker or a bandage, or a melted candy.
Colored transfer with no texture is usually dye from a new garment, or ink from a pen left in a pocket.
A dull, slightly tacky film across the whole drum is not a spill at all. That is fabric softener and dryer sheet buildup, covered in do dryer sheets leave residue.
Rust colored spots may be actual rust from a chipped drum coating, which is a repair rather than a cleaning problem, since a chipped drum will keep snagging and marking fabric.
Safety before anything else
Unplug the dryer before you put your hands or a cloth inside it. For a gas dryer, that is enough for cleaning the drum -- you do not need to touch the gas line.
Never use gasoline, paint thinner, acetone, lacquer thinner, or any flammable solvent inside a dryer. Vapor plus a heating element or an igniter is a fire and explosion hazard. This is the same rule that applies to clothing: gasoline or solvent on clothing never goes in a dryer under any circumstances.
Never mix cleaning products in the drum. Chlorine bleach with an acid or with an ammonia-containing cleaner releases toxic gas. Also skip chlorine bleach on a stainless drum -- see why chlorine bleach pits stainless steel.
Ventilate the room and leave the door open while you work.
How do you clean a dryer drum?
Unplug the machine, then work the residue with the mildest approach first: hot soapy water on a cloth, then a paste of baking soda and water for waxy marks, then a small amount of rubbing alcohol on a cloth for ink and dye. Wipe clean, dry the drum, and run a load of damp rags before real laundry.
Method by residue type
Melted crayon, lip balm or lipstick
Start with heat, oddly enough. Run the empty dryer on high for five to ten minutes to soften the wax, then unplug it and wipe firmly with a dry cloth or a paper towel while the drum is still warm. Most of it comes off as a smear.
Follow with hot water and dish soap on a cloth to cut the remaining oil. For anything stubborn, make a paste of baking soda and a little water, work it in with a soft cloth in small circles, then wipe away and rinse with a damp cloth. Baking soda is mildly abrasive, which is enough for wax and gentle enough for the drum coating.
Gum or adhesive
Chill it rather than heat it. Hold a bag of ice against the spot for several minutes until the gum goes hard and brittle, then lift the edge with a plastic scraper or an old credit card. Never a metal blade -- a scratched or chipped drum coating will snag fabric permanently. Clean the shadow with hot soapy water.
Ink or dye transfer
A small amount of rubbing alcohol on a cloth is the standard approach. Apply it to the cloth, not to the drum, work the mark, and switch to a clean section of cloth often. Rubbing alcohol is flammable, so use a small amount, keep the machine unplugged, keep the door open, and let the drum air out completely before restoring power.
Overall softener film
This one is not a spill, it is accumulation. Wipe the entire drum with hot water and a drop of dish soap, then a clean damp cloth, then dry. If the film keeps returning, the cause is dryer sheets or liquid softener, not the machine. While you are at it, wipe the two small metal moisture sensor strips near the lint opening with rubbing alcohol -- softener film on those makes automatic cycles shut off early.
Always run a test load
This is the step people skip and regret. After cleaning, put four or five old damp rags or a set of dark towels you do not care about in the drum and run a normal heated cycle. Then inspect them.
If anything transfers, the drum is not clean yet. Repeat the process and test again. Only then go back to real laundry.
Finish the job outside the drum
Residue rarely stays in one place. Wipe the door seal and the inside of the door. Pull the lint screen and check for wax or ink on the mesh. Then clean the lint trap and its housing, because whatever melted in the drum also went past the screen.
If crayon or wax went through the washer first, that machine needs attention too. A hot empty cycle with an oxygen bleach booster is the right follow-up; see how to use oxygen bleach at home.
FAQ
How do you get melted crayon out of a dryer?
Warm the empty drum for five to ten minutes, unplug the machine, and wipe the softened wax off with a dry cloth. Follow with hot soapy water and, if needed, a baking soda paste. Then run a load of old damp rags to confirm nothing transfers.
Can I use bleach to clean my dryer drum?
Avoid it. Chlorine bleach can pit and discolor a stainless drum and can damage a painted drum coating, and its fumes have no business in an enclosed appliance. Hot soapy water, baking soda paste, and a small amount of rubbing alcohol cover nearly every residue.
Is it safe to use rubbing alcohol inside a dryer?
In small amounts on a cloth, with the machine unplugged, the door open, and the room ventilated. Let the drum air-dry completely before restoring power. Never spray alcohol into the drum, and never use gasoline, acetone or paint thinner in a dryer at all.
Why do my clothes keep coming out with marks?
Either residue remains on the drum, something is still in the lint housing, or the drum coating is chipped and snagging. Run the damp rag test first. If the rags come out clean and clothes still mark, inspect the drum surface for chips and the seal for a torn edge.
How often should I clean the inside of my dryer drum?
There is no routine need unless something spills, but a quick wipe with hot soapy water two or three times a year keeps softener film from building up and keeps the moisture sensors reading accurately. Clean immediately after any spill or melt.
What if the residue will not come off at all?
Stop escalating chemicals. Repeated gentle passes with a baking soda paste do more than one aggressive attempt, and aggressive attempts damage the drum finish. If the mark is under the coating rather than on it, or the coating is chipped, that is a parts issue for a technician.
The whole-house equivalent of this routine is covered by house cleaning services.
If the laundry room has other problems stacked behind this one, it may be worth handing the whole room off. Every home is different, so the real number depends on size, condition, and what you want covered. Get a quote and we will walk you through it.