i'm looking at fitting an auto clean out setup on a water tank.

nothing new thats discussed here before and i've done it before. however this ones a bit different in that its a storm water detention tank and i am looking at putting the syphon break hole lower down than normal. by putting the hole down lower i'm trying to pull extra water out of tank when it overflows, so its got a little bit of space for the next bit of rain. (the normal outlet will take a day to empty the tank). also that will give it more full on pull to help clean the tank and push the crud down 20m of pipe.

now what i'm not sure on is if having the hole down lower will cause an air lock in the overflow pipe. any thoughts?