Normal food grade 20 litre bucket to create a simple filter,

Drill with 30mm holesaw and fit a 25mm Hansen bulkhead.

Side on view

Where does the number 8 wire go?

That would be the handle on the bucket lol.

Fitted water inlet plumbing, the pond water level overflow is higher than the bucket but base of pond is lower than the bucket

Cut sponges to fit tight in bucket, they will be above the pump

Operational

From bottom of pond to top of bucket, bucket 2/3rds full  so when pump stops bcket fills to just above the bulkhead with excess water from overflow

Livingart - you should run DIY fish keeping classes.

SHouldn't you reverse the order of the sponges and filter wool?  THe filter wool would clog up in a day or two while the sponges would still be nice and clean?

Yes normally but the sponges are quite an open cell so using them more for housing bacteria 6 medium sized Long neck turtles in there and filter wool has lasted a week so far.

Be interesting to see what it looks like in another 25 weeks, about my normal maintenance interval on my filters.

My geto version