TL;DR
The black specks that come out of a squirt toy are mildew growing inside a sealed, permanently wet chamber that never sees light or air. You can clean the inside with a soak and repeated squeezing, but the interior of a squirt toy is almost impossible to verify as clean. The reliable fixes are sealing the hole shut before first use, or replacing the toys with solid ones.
What the black stuff is
Every squeeze pulls water into the toy. Almost none of it ever comes back out.
That leftover water sits in a warm plastic chamber with a little soap, skin cells, and whatever else was in the bath. There is no light and almost no airflow. Mildew and bacteria grow on the interior walls as a slimy film, and pieces of it break loose and get squirted out.
People call it black mold, and it may include mold species, but it is a mixed film of mold, mildew, and bacteria rather than one identifiable thing. The label matters less than the fact that it is coming out into a child's bath.
The same trapped-water mechanism causes the black spots under a suction cup mat, described in how to clean a rubber bath mat and its suction cups.
How do you clean bath toys that squirt black?
Fill each toy with a cleaning solution through the hole, squeeze it repeatedly to scrub the inside, then let it soak, and flush with clean water many times until the water runs clear. Squeeze out every drop and dry the toy hole down. If black material keeps returning, replace the toy.
The cleaning method, in order
1. Squeeze out all the old water. Over a sink, repeatedly, until nothing more comes out.
2. Fill with a cleaning solution. Two options, and use only one.
A vinegar solution of one part white vinegar to two parts warm water is the milder choice and is often enough. It handles mildew film and mineral deposits.
A diluted bleach solution of about half a teaspoon of household bleach per quart of water is stronger for badly contaminated toys. Ventilate the room and rinse afterward far more thoroughly than feels necessary, since these toys go in a child's mouth.
3. Squeeze the toy repeatedly while it is full. This is the actual scrubbing. Twenty or thirty squeezes, forcing solution against the interior walls.
4. Let it soak. Fifteen to thirty minutes for vinegar, five to ten for a diluted bleach solution. Do not leave bleach in a toy for long periods.
5. Flush with clean water many times. Fill, squeeze, empty, repeat until the water coming out is completely clear and there is no smell at all.
6. Squeeze out every drop and dry hole down. Store them upside down on a rack.
Never mix cleaners. Bleach with vinegar releases chlorine gas. Bleach with ammonia releases chloramine gas. Bleach with rubbing alcohol produces chloroform. Pick one, rinse thoroughly, and never combine them in one container or one session.
A dishwasher top rack works for some solid toys, but it does not reliably clean the inside of a squirt toy, because water does not circulate through a small hole under pressure. Check that the toy is rated for it, since heat warps thin plastic.
Sealing the hole shut
This is the fix that actually works, and it is what many parents end up doing.
Buy the toys new, or clean and dry existing ones completely first. A toy that is already contaminated inside and then sealed just traps the problem permanently.
Once the toy is fully dry inside, which can take several days, plug the hole with a small dab of waterproof adhesive or aquarium-grade silicone sealant. Follow the product label, cure it in a ventilated space away from children, and give it the full cure time before the toy goes near water.
The toy no longer squirts. It becomes a floating bath toy that stays clean, and that trade is worth making for most families. Check the seal periodically, because if it fails the problem starts over.
Are moldy bath toys dangerous?
For most healthy children, occasional exposure to the film inside a bath toy is unlikely to cause harm, but it is not something to accept. Children mouth bath toys, and the film contains bacteria and mold. Clean the toys, seal or replace squirt toys, and talk to a pediatrician about any child with asthma, allergies, or a weakened immune system.
We are not in a position to give medical advice here. What we can say is that removing the exposure is easy and there is no reason to leave it in place.
Source: U.S. Environmental Protection Agency guidance on mold and moisture in the home
Buying toys that do not have the problem
The whole issue is designed into squirt toys. Buying differently ends it.
Solid toys with no hole. Molded rubber or plastic with no cavity. Nothing gets inside, nothing grows.
Toys that open. Some manufacturers now make bath toys that come apart for cleaning. These are worth seeking out.
Silicone toys. Nonporous, dishwasher safe, and fast drying.
Cups, boats, and stacking toys. Open shapes that drain and dry completely. Children generally like them at least as much.
Storage that keeps everything drier
Where the toys live between baths matters as much as how they are cleaned.
Use a rack or a mesh bag that drains, hung outside the tub. A bucket on the tub floor is a reservoir.
Squeeze the water out of every squirt toy at the end of the bath rather than tossing them in wet.
Run the exhaust fan during and after baths. A bathroom that dries out in an hour is a completely different environment from one that stays humid all day.
Rotate a smaller number of toys and clean them weekly rather than keeping thirty of them permanently damp.
The same drainage-and-airflow logic is what fixes the items in how to clean a soap dish that stays slimy and how to clean a loofah, bath pouf, or sea sponge, and it runs through cleaning the personal items you use every day.
When to just throw them out
Replace a squirt toy when black material keeps coming out after a thorough cleaning, when you can see film through the plastic, when the toy smells, or when it has cracked.
Toys are inexpensive and the inside of a squirt toy cannot be inspected. If cleaning has not clearly solved it, replacing is the honest answer.
Discolored or crumbling plastic is a replacement regardless of the mildew question.
FAQ
What is the black stuff coming out of bath toys?
It is a film of mold, mildew, and bacteria growing inside the toy, in water that gets sucked in through the squirt hole and never fully comes out. The interior stays warm, wet, and dark, which is ideal for growth. Pieces of that film break loose and get squirted back into the bath.
How do you clean mold out of squirt toys?
Fill each toy with a vinegar solution or a very dilute bleach solution, squeeze repeatedly to scrub the inside, soak briefly, then flush many times with clean water until it runs completely clear with no smell. Squeeze out every drop and dry hole down. Never mix cleaners.
Should you throw away moldy bath toys?
Often yes. The inside of a squirt toy cannot be inspected, so there is no way to confirm it is clean, and children mouth these toys. If black material returns after a thorough cleaning, or you can see film through the plastic, replacing the toy is the reliable answer.
Can you put bath toys in the dishwasher?
Solid toys rated for it can go on the top rack, but a dishwasher does not reliably clean the sealed interior of a squirt toy, because water will not circulate through a small hole under pressure. Check the toy is dishwasher safe first, since heat warps thin plastic.
How do you seal the hole in a bath toy?
Clean and dry the toy completely first, which can take several days, then plug the hole with a small dab of waterproof adhesive or aquarium-grade silicone sealant and let it cure fully before use. The toy stops squirting but stays clean inside. Sealing a contaminated toy just traps the problem.
How do you stop bath toys from getting moldy?
Squeeze all the water out after every bath, store them in a draining rack or mesh bag outside the tub, and run the exhaust fan so the room dries. Better still, choose solid toys, cups, and boats with no interior cavity, which cannot develop the problem at all.
Bath toys are a ten-minute job. A bathroom that stays genuinely dry and clean is a bigger one. If you would rather hand that off, get a quote or read more about house cleaning services.