After the filter issues I had last summer, I made up a cleaning device using a length of 3/8” copper pipe, a length of clear braided hose, a small 12v vacuum (air) pump off eBay, and a large 25 litre plastic container. It was reasonably successful apart from the catch container having a tendency to collapse under vacuum - I really need some sort of much heavier duty thick walled container.
Here’s the muck that came out. These are 10 litre containers, first lot on the right. If you look closely at the right and centre containers, you can see the water at the bottom. Left it to settle out for a couple of weeks, decanted the clean stuff off and returned that to the tank. Had a proper primary filter fitted as well.