I have gotten into the habit of creating Follow-up Tasks, rather than continuing to add things to an enormous Waiting For list. This has been working much better for me.
So, at the time that I delegate something (whether by e-mail, or call, or whatever) I create a task in my normal task list (in this case Outlook) which does not appear until the date I feel is appropriate to follow up with the individual to whom the task has been delegated. Until then, it remains out of sight (I use the Start Date field to filter out future tasks).
You could do the same with ToodleDo, or with Taskwarrior, or probably with a dozen other free tools if you're willing and able to try others and if Google Tasks doesn't offer you the functionality to make this work.
Example scenario: today I delegate a task to "Bob" and I think to myself that if I haven't heard from him by Monday, I'll follow up with him then. In my task list I'll create a task titled "F:Bob: Re: Fixing the door frame" and with a Start Date of Monday. Until that day arrives, I won't see this task. On Monday when I look at my list during my normal routines, it will appear; if I've heard from him already I'll just close/complete it. If I haven't, then I'll contact Bob.