Neil wrote:
Hi,

I went to bed last night, to the sound of dripping and found out it
was from just alongside my loft hatch - set out a drip-catcher and
went to bed. This afternoon I took a closer look. It seems that the
wet patch (or the only one I can see) is on one bottom corner, a
corner where the loft hatch might rub on the tank and where it is
definitely dripping from.

I've taken some pictures:
http://www.kepiernet.f2s.com/loft/subalbum_1.html

Pictures 6,7 are the best of what seems to be the 'hole'.

Any idea whether this looks rodent-caused? and perhaps more
importantly whether the tank should be replaced in a situation like
this, or whether I could just get some gungy stuff to fill the hole?
(maybe even while full of water?)

Friends/family are shouting at me to get a plumber out, and while I
can't see the rest of the loft very well, this seems to be the only
noticeable problem.

Thoughts?

Patch it up, lay some poison (possibly rat - difficult to appreciate the
size of the gnawing marks), when the poison is being no longer taken
consider replacing the tank. Don't replace it until you've eradicated the
pest.

Leave poison up there permanently.