Here's a simple way to use voting to clean up some crap:

 1. In the search box, enter:  votes:0 answers:0
 2. Click the "Newest" tab and scroll down until you're looking at questions that are at least a day old
 3. Click on one that looks bad (based on the excerpt), read it.
 4. If it really is bad, vote it down.

After 30 days, questions with no answers and negative scores are automatically deleted.

The "official" meta post with the auto-deletion rules was recently updated: http://meta.stackexchange.com/a/92006/130540

And after reading the recently-added section of that meta.SO post, really bad questions could be cleaned up even faster:

 1. In the search box, enter:  closed:yes votes:0 answers:0
 2. Click the "Newest" tab 
 3. Click on one that looks bad (based on the excerpt), read it.
 4. If it really is bad, vote it down.

After 9 days, closed questions with no upvoted answers are automatically deleted.

Update:
-------

I've been searching for 

closed:yes answers:0 score:0 migrated:no

for a while and downvoting the questions I think are crappy (most of the results).  Note that score:0 matches only score=0.

The auto-delete runs early Sat morning, so last night I checked:

closed:yes answers:0 score:-1 migrated:no

And got 1493 results.  (Note that score:-1 matches score>=-1, but there aren't too many closed q's with no answer and upvotes.)  This morning, there are only 1284 results, so 200 crappy questions have gone away!

As far as I can see, duplicates with no answers and -1 or less get deleted the same as other close reasons.  (Unless they were merged.)