You can be the original owner, or you can buy used LEGO bricks that have turned into grubby chunks of dirt over the years. It will not be so difficult to clean them, but with a large collection of parts it will take a lot of time. After cleaning your LEGO blocks, you can also try to restore them to their original color, which was lost due to sun fading.
Steps
Method 1 of 3: Hand Wash

Step 1. To minimize possible damage to parts, you should use this method
This method will take more of your time than the others, unless the LEGO is just a little dirty. Use this method when cleaning your favorite or collectible LEGO pieces to protect them from accidental damage.

Step 2. Clean non-waterproof parts with a dry towel or toothbrush
Set aside any decal or patterned parts, as well as complex components that should not be disassembled, such as swivel discs. Use a dry towel to clean them or remove stubborn dirt with a new toothbrush.
Delicate electrical parts can be cleaned with alcohol wipes

Step 3. Divide all other blocks
Separate all water-resistant parts from each other, unless they are stuck. Be sure to disassemble all prefabricated parts such as tires.
If you have a large collection of parts, place them in separate containers of 200-300 pieces

Step 4. Rinse the parts in soapy water
Place the disassembled LEGO bricks into the container. Cover it with lukewarm water and add a little dish soap or other liquid detergent. Rinse the parts gently by stirring with your hands.
- Never use a cleaning agent containing bleach.
- Never use water hotter than 40 degrees Celsius.

Step 5. Add wine vinegar (optional)
If the parts smell bad, or if you want to sanitize them, add wine vinegar to the water. Use about ¼ - ½ of the water available in vinegar.

Step 6. Leave the parts to soak
Let the parts soak for at least 10 minutes and then check them. If the water becomes very dirty, replace it with fresh, soapy water and let it soak for another hour or even overnight if convenient.

Step 7. Rub the details if necessary
If the parts are still dirty, you may need to rub them with a new toothbrush or toothpick to clean the grooves.
Transparent plastic parts such as window panes are easily scratched. Only rub them with your fingers

Step 8. Rinse the parts
Transfer the LEGO pieces to a strainer or colander and rinse with cold water to rinse off any soap and loose dirt.

Step 9. Dry the parts
Alternatively, you can scroll through the parts in a salad dryer to get rid of excess water. Then spread the wet blocks in a single layer on a towel so that the water can drain down. To speed up the drying process, turn on the fan to blow over the parts.
Do not use a hair dryer, it can ruin your LEGO
Method 2 of 3: Washing in the washing machine

Step 1. Follow these directions at your own risk
LEGO Customer Support warns people against using washing machines as there is a risk of melting and breaking parts. Many LEGO bricks can come out of the washing machine unscathed, but that doesn't necessarily mean your blocks will be able to withstand the test of your washing machine.

Step 2. Separate the parts
Separate the parts from each other, unless they are hopelessly stuck together with dirt. Set aside all printed, moving parts, electrical parts, and transparent parts. All of the above should be wiped off with a dry towel or alcohol-based wipes so as not to damage.

Step 3. Place the parts in a laundry net or pillowcase
The laundry mesh will prevent your washing machine from getting jammed with LEGO pieces and will minimize possible damage from drum rotation, but the parts may be scratched. If you do not have a special mesh for washing clothes, you can use a pillowcase, just do not forget to close the zipper on it or tighten the inlet with an elastic band.

Step 4. Set the washing machine to a delicate wash cycle using cold water
Use the most gentle wash program available with your washing machine and use only cold water. Temperatures above 40 degrees Celsius can melt LEGO pieces.

Step 5. Add liquid detergent
We recommend using a mild liquid detergent rather than powder to avoid scratching the parts. If you're having trouble finding a gentle detergent, look for products that claim to be environmentally friendly.

Step 6. Leave the parts to dry
Spread the parts out on a towel so that the water can drain off. Ventilate the room to speed up the drying process, but keep the parts away from heat. Depending on the humidity of the air, the parts may dry for 1-2 days.
Method 3 of 3: Recovering the color of faded LEGO pieces

Step 1. Pre-wash the parts
This method can reverse sunlight-induced fading, but it is not intended to wash off dirt. Before using it, use one of the above LEGO cleaning methods.
In this case, after washing the parts, there is no need to dry them

Step 2. Place the parts in a transparent container
Sunlight is an important part of this method, so use a clear glass or plastic container. Place it in a sunny place, but keep it away from children and animals, as you will be using inedible products.
- Since hydrogen peroxide only reacts in the presence of ultraviolet light, only sunlight or the light of an ultraviolet lamp can be used.
- Do not use this method on decal parts and electrical parts.

Step 3. Fill the parts with hydrogen peroxide
Use a regular 3% peroxide solution from your pharmacy. You will need enough of it to completely fill the discolored blocks.
Although 3% hydrogen peroxide is safe for your skin, wear gloves and goggles to minimize skin contact. Be careful not to get the peroxide in your mouth or hair. Children should ask adults to perform this procedure

Step 4. Weight the large floating parts
Some of the LEGO parts can float in hydrogen peroxide. Use a heavy object to drown them.

Step 5. Stir the parts once an hour
Stirring the parts with a stick or gloved hand will release the bubbles that form and cause them to float. For best results, try to stir the parts about once an hour. If parts are left to float on the surface for too long, a white streak may remain along the water line.
If after an hour no bubbles have formed, then the peroxide has disintegrated and predominantly turned into water. Drain and try a different bottle of peroxide

Step 6. Rinse and dry the LEGO bricks when they are colored again
The process usually takes about 4-6 hours. It all depends on the strength of the sunlight and the freshness of the hydrogen peroxide. Then place the parts in a colander, rinse and let dry.
Advice
- Clean electrical parts with alcohol wipes.
- Chaotic movement of blocks in the washing machine can lead to their pooling. One person even sold these random LEGO creations.