As you wash finished prints with IPA/Ethanol, the uncured resin will be stripped off and mixed with the alcohol. As time goes on, the alcohol will be saturated with more uncured resins to the point where it becomes counter-productive to wash in it. Here is how to make the best use and dispose of dirty alcohol with resins.
Use it as the first wash.
It is an excellent practice to have two buckets of alcohol, one is dirtier, and one is clean and fresh alcohol. The purpose is to use the cloudy alcohol to do the first wash to remove most of the uncured resin before moving to the pure batch for the final wash. This will make the alcohol last longer by keeping the clean batch fresh and having a way to use dirty but still usable alcohol.
(Note: PS: The picture comes from VOG video, link youtube.com/watch?v=5U1IshPqmak)
At some point, the dirty alcohol will be so cloudy that you can no longer use it to clean effectively. You will have two options. Recycle if your alcohol is IPA or dispose of.
You can consult the excellent video by VOG
Do not dump dirty alcohol into sewage! It can have devastating on marine lifeforms!
The proper way and most energy efficient to process IPA/Ethanol is to let it evaporate via sunlight. This will cure the resins in the alcohol while removing the alcohol. Please do this outdoor, not in an enclosed space. Do not try to boil the dirty alcohol. It is not a safe practice. For places that do not get much sunlight or during the Winter season, IR light can help remove the alcohol quickly.