It has come down to threats, help

My life is being taken over with the cleaning of toy messes.  I just can't keep up with Liam and Marlo.  I tried the "you must clean up your first mess before you make another mess" rule, but that's not going so great.  Half the time they are (well, mostly Liam, but Marlo joins in) moving on to the next mess before I even realize that mess number 1 is uncool and a new mess has been discovered.  Or Liam combines the messes.  One of his favorite games is 'Garbage Man' where he takes a bunch of toys and dumps them into a pile and puts them into bags and re-dumps them (like a garbage truck). The other half of the time, Liam whines  so much about cleaning up that it just drives me nuts.  So then I tell him that I am going to clean up his toys and throw them away.  Of course this sends him into a crying fit and Marlo starts to cry because she doesn't like to see him cry and chaos and unpleasantness is brought into our day - times 5 because this happens multiple times a day.

So, I 'd like to know if any of my readers have any suggestions.  I don't want to reward him with a treat or something because cleaning up his toys just needs to be part of his everyday "to-do" list like brushing his teeth and taking a bath.  But I want a better solution than the threat.  Granted, the threat works, but I hate getting to that place where I have to make him cry to do something.