Graham, check out this web site http://www.mvwgs.org/filter.htm .
I made this filter just Saturday 6/21/03 and it took about 2 hours including
the trip to Loews and cost just less than $20.

I made sure all the filter pieces fit very snugly together to eliminate the
possibility of accidental bypass or channeling.

Four days later and my water is sparkling clear. Never was that clean before
as I had to clean the filter (Pondmaster 1000) about every 5-7 days and
after 3 days the flow was considerably reduced.
BK

"Graham" wrote in message
...
Has anybody got a good design for a filter system for a 300 gallon system.
My finances will not run to a proper filtration system and was looking at
using 25/50 gallon water tanks.These will be fed from a 4" bottom drain.
Any help appreciated