What you don't want to hear is that how these situations are usually managed is by not letting them grow so big. But I'm afraid that is the case.
The Pragmatic Programmers advise us Don't live with broken windows. The point being, that if we leave something broken instead of fixing it then other things will be left and before we know it we have 480 items on our TODO list. Plus, there is a danger that some part of our application will come to rely on the "broken" behaviour, so when we address the TODO item we also have fix that as well.
Not everybody can live up to the Pragmatic Programmers' high standards. An alternative approach is to have a list of stuff which needs to be worked on (sometimes known as the Kaizen list). People who are blocked on their assigned work can pick up one of those tasks.
As for your current situation....
I have a rule of thumb which states that nothing can be done in less than half-a-day: not once you include source control, documentation, discussing the change with Bob, etc. Of course, my rule of thumb doesn't apply to truly trivial tasks, but if these tasks were truly trivial they would have been fixed on the spot, not marked as TODO, right?
So you're looking down the barrel of 240 days of effort. If lots of those tasks can be combined into a single fix then you can reduce the per task overhead. But first you've got a chunk of work just to sift through the tasks, categorising and prioritising them. This is why thay call it "technical debt": the longer we leave it the more it costs to fix, and it has the compound interest rate of the average doorstep loanshark.
Unless you have a very understanding project manager/paying customer I think you will have to accept that you aren't going to be able to clear all these items. So you need a brief triaging exercise: assign each TODO into one of three categories:
- Stuff that is intolerable and needs
to be fixed right now
- Stuff that ought to be fixed as and
when there is an opportunity
- Stuff that you're just going to have
to live with
Good luck!