Sight tube indicator

[AntarcticPilot]

A belated wrap up on this! What we eventually did was to put white tape on the side of the sight tube away from the viewing direction. This makes the level of the diesel much easier to see, using a torch if necessary. Diagonal stripes would perhaps have helped as well, but weren't available when we did the job.

 

[Seashoreman]

That sounds like a simple enough solution that I may try myself, ta.

 

[Ravi]

Have you seen the Truma gas level checker that I wrote about in YM? http://www.obelink.co.uk/car-caravan-accessories/gas/truma-levelcheck.html I used mine on the diesel tank and found it worked well for a steel tank but not for a plastic one. Not very cheap, although cheaper than a proper tank gauge, and it can be used for gas also.

I see the OP has sorted this but for the benefit of anyone searching for solutions in the future, I can +1 vyv's suggestion.
With a shallow tank and bent input hose limiting my options (and being reluctant to fit a sight tube), I bought a similar handheld gas measuring device. The one that I got is cheaper but after a bit of practice, I seem to have got the knack. So, if you have a metal tank, one of these hand held gas gauges is definitely worth trying.

 

[Robin]

The ideas like the diagonal strip or white paint behind the tube assume that the reading direction is normal to the tank wall. Sadly, it isn't on mine! The site-tube lives in a gap about 6 inches wide between the cockpit locker and the fuel tank, so the reading direction is parallel to the tank wall, and there's nothing behind it.

What I really need is a source of suitable coloured beads; if there's such a thing as a fluorescent one, that would be handy!

fluorescent beads about 5mm dia are common in fishing tackle shops as 'stops' before and after swivels etc. I bought a bunch of them in France way back and they are sold here even in Walmart's fishing aisle. I used them on a home made sight tube on a water tank on my then W33, no idea if they would react with diesel mind. My W33 had a sight gauge with a push tap at it's base, I managed OK with a torch but also had a dip stick as the ultimate option. If you get stuck PM me and I'll put a couple in the post.