Diesel fuel tank replacement and pipe work advice...

[PetiteFleur]

Seriously consider a ready made tank from Vetus, Plastimo. Caktanks or TekTanks(they do a ready made range) or others. Not a huge variety of shapes, mainly rectangular BUT considerable cheaper than a custom made tank from TekTanks - all assuming these tanks will fit your space. They come with an inspection tank and all fittings etc and can have a gauge fitted.
Fit all new pipework etc and make filter accessible. I replaced a leaking steel tank with a Plastimo tank, only 19 gallons as against the original 40 gallon but had to cut the old tank up insitu as it was impossible to remove in one piece. I have over 24hrs motoring which is more than adequate for me.

 

[Tranona]

Have a look at the photo in the original post. Not a suitable application for a standard shape tank - at least in the location of the original.

 

[aquaholic]

thanks for all the helpful comments, after removing the tank and cleaning with various methods I have satisfied myself that its fine to reuse and have had new fuel lines made up as well as getting new tank fittings, although just to make sure I will treat with Marine 16 or similiar.

 

[macd]

Tek Tanks recommend against a bottom drain for reasons of possible leakage, which makes sense to me. The alternative is a dip pipe from the top right to the lowest point of the tank, which you can attach a pump to (could even permanently install one of those brass hand-pumps if you like to regularly check).

Fitting a new tank without an inspection hatch would be bonkers, obviously.

+1 to that and all similar suggestions.
I built an epoxy GRP tank a decade or so ago with just such a dip-pipe, leading to a length of hose with a tap at the end. Once primed (yuch!) it stayed primed -- so actually no need for a dedicated pump. Checking for crud/water at the bottom of the tank was so quick and simple, it became a routine.

As fuel formulations change, the problem of diesel bug is likely to increase, not lessen. To fit a tank without a convenient means to drain it is plain daft (yet still most boat manufacturers do it).