As you know, it is recommend to do water change once a week. If you have mosquito larvae problem, water change twice a week is a must. But, it is troublesome and time consuming if you have few water tray that filled with 20pots CPs in each.
What you can do to suit yours lazyness is...
1. go to hardware shop, buy a plastic chock (normally is reddish pink color).
2. buy a drill head (for cement use) that well fit the plastic chock.
3. drill a hole at buttom of yours water tray. Get the plastic chock to "close" the hole. Refill water to the tray and test it. If no leaking, means, it is done.
I did the below twice a week.
1. at night, I take out the chock and lets ALL water flow out from the tray.
2. Next morning, close the hole with chock and refill water.
Reason:-
1. water change to remove possible mineral that forming in water
2. kill/remove mosquito larvae from water tray
P/S : I still will wash/clean the water tray/pots twice a month, when im free...