Now that mines have the target slider to optimize them for truck use it would be nice if we could do the same with smokestacks. A slider with a value that not queue trash delivery until there is at least X free space. Setting this to 5 would allow for full truck loads of waste deposited into the smokestack.
It seems that smokestacks in general are a little strange when it comes to trucks. I often see trucks in use to empty mines but rarely see them deliver waste to the smoke stack with employees preferring to carry the waste by hand (despite adequate transport hub coverage).