The first photo attached shows diesel bug build up after 2 years in a Bavaria ( not mine) based in Malta. Never had tank cleaned ( 2002 model) and never had fuel additives. The owner replaced the strainer for the next season.
I bought the same type of strainer for 4 euros after diesel bug stopped my engine on a trip from Sicily to Malta. Had a raisin sized lump clog the off/on switch. Second Photo shows the lump blown out with compressed air. After I installed a new strainer and ran the engine for about 1/2 hour I had some bug visible in my strainer. I put some Startron, an enzyme based treatment, in the tank and then motored for 9 hours back to Sicily. By the time I arrived back, there was no gunk in the strainer and the fuel looked clean. I then checked the tank and found it was clean. This was the second bug attack, the first 2 years before this on the first trip of the season in Turkey. Again, the bug blocked the off/on switch. It appears that almost all bug attacks in Europe happen early in the season. Cold, motionless tanks during the winter layups seem to grow bugs and possibly don't allow the enzyme type preventative treatments from working. I've had no problems in the 4 years since, bearing in mind that living in Australia means no winter layup, all year sailing and no FAME in the diesel.
Yachting Monthly had a great article on the efficiency of Biocide and Enzyme fuel treatments a few years ago. I bought Startron based on those tests.
I understand that some boats stop due to a blockage in the fuel pickup lines and most boats stop due to clogged filters but the small size of the off/on switch in Bavarias seems to catch bug before anywhere else. This type of strainer should give a good visual clue as to any problems before they arise. You will get enough Gunk out of one of these strainers to make a vegemite sandwich before your off/on switch is likely to be blocked.
Craig
"Shirley Valentine"
Gold Coast
Australia