When trying to suppress revolts, while you can recruit just about anything to do so, you have to remember that it helps to bring the population down a bit as well. All units take away from a city's population when recruited, but Peasants, Warbands, Phalanx Pikemen, and SSP/Royals take far more than all other units. A full
50%, in fact.
So, if you chose to fill up your recruitment queue with standard (40-man) units, you will be taking between 180 and 1440 men (depending on your unit size setting). However, if you fill it up with Peasants (or another, 60-man unit), you will be able to take a good
2160 men out of the population; just like that. Generally, simply filling up the queue with Peasants is enough to improve public order. This gives you a bit of "breathing room"; so you can wait for troops to arrive from other settlements or simply wait for the Peasants to finish training and have them give you the "Garrison bonus" directly.
Generally you wont have a city revolt due to squalor early in the game, so by the time populations get that high, the fighting will probably be far from the cities in question. As such, you probably wont need to defend those settlements from other factions anyways.
I exterminate all cities I capture, so I usually only have squalor in my core provinces, so if I need to worry about defending them, I'll probably have bigger problems than worrying about revolts