It's probably better to do a 'kill -TERM' than a 'kill -KILL', but anyway...FYI, you can also specify the job number in a kill, ex:
% touch foo
% touch bar
% tail -f foo
^Z
Suspended
% tail -f bar
^Z
Suspended
% jobs
[1] - Suspended tail -f foo
[2] + Suspended tail -f bar
% kill %1
% jobs
[1] Terminated tail -f foo
[2] + Suspended tail -f bar
% jobs
[2] + Suspended tail -f bar
%
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Also, you can just logout once more after the warning and it'll let you log out w/ suspended jobs:
% tail -f foo
^Z
Suspended
% logout
There are suspended jobs.
% logout
(disconnected)