Vortex Tank: anyone use these?

[Taoism]

I inherited a tiny pond with my house when I moved out here to Ottawa.  It's maybe 4'x2.5'x18" deep.  I would like to be able to winter fish in the pond, but as it currently exists that is not possible.  So, I am trying to understand how build a pond so I can potentially rip mine apart and redo it slightly larger and much deeper.

I have been reading the pages on this site about pond construction:
http://www.clarkekoi.com/ConstructionFundamentals.html

I am trying to understand vortex tanks.  In principle, it seems easy enough.  Dirty water enters near the bottom-to-middle of the tank such that it creates a laminar flow and that will induce particles to settle at the bottom.  Near the top of the tank is an outflow to move water with greatly reduce particles to another stage in the filtration setup.

Am I correct in assuming that if nothing is done the matter at the bottom of the vortex tank will simply continue to build up and will not break down on it's own?  You need a separate release from the bottom of the vortex tank to dump the sludge?  If so, how would this be handled in an urban situation?  I imagine just dumping the sludge in your back yard would result in an ungodly smell and mess.

It also seems that the best way to do these is a gravity-based system (bottom drain in pond uses gravity to pull waste from pond and into vortex tank?).  I'm not sure how doable that is in a lot of urban back yards.  Would a pump work for this?


Have any of you done this type of system?  What would happen in the winter?  Simple shut off all the pumps and hope they don't freeze and burst?