UGF questions

I inherited an under gravel filter with my cichlid tank. I cleaned
it and set it up to run and it's going fine now -- run by a powerhead.

1. How does it work? I know the debris gets sucked down through
the gravel, pulled up a stand pipe and then spit out by the
powerhead. Doesn't that simply spit out the debris back into the
tank? Nothing was taken out by the filter? (There are no
mechanical filters along with the UGF.)

2. The debris spit out is picked up by a hang on back power filter.
Is that how people run a UGF?

3. How do I take care of a UGF? (No directions came with it.)
Vacuum the gravel weekly? Yearly take all apart and clean?

4. What are the advanges filter-wise to a UGF?

Any links would help too.

Thanks in advance.
coolchinchilla