Tacet

It would make life exciting if you dropped the bung - but think how good you will feel if you don't. Sealing the filler cap and the vent would slow the rate of discharge and generally make life easier. You could replace the bung with a valve, with the outlet side closed by the bung (or another bung) for future ease. BSS says something about a requirement to use a tool to empty the tank - not just a permanently fixed lever.

A drain point at the lowest part of the tank will remove the water and much of the crud; the small amount remaining will probably not get lifted up the dip pipe and if it is, the filters should cope. For the economically minded, if a reasonable quantity of fuel/muck is drawn off into a container, it can be left to settle for a day or so. The clean diesel rises to the surface and can be returned to the tank with care. .

On numerous visits, the only advice given by my grandfather's GP was "no washing-up for a fortnight"

According to the DFT, that part of the M5 has an annual average daily flow of around 100k (both directions - which seems plausible). Or around 36m per annum. It seems it is visible from all lanes. The basic vehicle types are available, which would allow you to have a stab at the number of person passing each day, but keeping it simple, a car typically has (but maybe not on the M5?) 1.5 occupants; some will be dozing or looking elsewhere etc so maybe a total of 50m per year. More tricky is how many (different) people in a year, which is the question posed. My guess is a lot less than 50m; possibly high seven figures?

Only if Goliath was selected as part of the random sample. He should know. It is hardly realistic to ask everyone in the country (world?) how many visits they have made - thus sampling is the only reasonable option. A statistician should be able to calculate how large the sample needs to bee in order to achieve a particular level of confidence that the extrapolation falls within a defined range. Whether the sample was sufficiently random, whether the questions asked were fairly phrased, whether the responses given were accurate and properly recorded and whether I believe the outcome are different matters

The Institution of Engineering and Technology link It is reported that expanded polystyrene is most affected, but it can also occur with ABS or polycarbonate. It is stated by some manufacturers that modern PVC sheath compounds no longer react with expanded polystyrene, but if PVC sheathed cables are expected to be in contact with expanded polystyrene or other similar materials the advice of the cable manufacturer should be sought for the design

Sorry - I had indeed misunderstood your earlier reply

I think it is considered too tempting for the insured to net benefit from an insured event. Suspicious people, the insurance industry. As far back as 1774 The Fires Prevention (Metropolis) Act 1774 made (still extant), provisions to “to deter and hinder ill-minded persons from wilfully setting their house or houses or other buildings on fire with a view of gaining to themselves the insurance money” by requiring the proceeds of insurance to be laid out on rebuilding. So no option to torch, take the cash and run. Doesn’t apply to boats, though.