On Sun, 6 Jun 2021 10:17:44 +0100, newshound
wrote:

snip

I'd cut several 100 mm long strips of CSM about 20mm wide and with the
stub held securely in place, glass the strips round the pipe like 'L
brackets' and flower petals and do the same again, overlapping the
first layer and then a circular collar over that with the middle cut
like a star (out to the 68mm diameter) and then a band round the stub,
to just pin down any lose ends (woven roving / bandage better than CSM
for that last bit. I probably have some here you can have (stick in
the post etc)).


Or, for less effort, you could use a 3 inch bulkhead fitting or tank
connector (same thing, two different names) connected with flexible
hose. You might get away with a 2 inch.

I think Tim was quite specific in his requirements (if not directly
mateable to 68mm stuff). ;-)

Also, if he does line this tank with fibreglass he might need to glass
in a smooth collar of some sort if using a bulkhead / flanged fitting,
or use some additional sealant to ensure it seals against the back of
fibreglass?

I made an interesting discover the other day. I needed to fit some of
this stuff (two inch, actually) over the threads of another fitting that
was just too big. I popped the end of the hose in boiling water for a
minute or two and it became soft enough to push straight on.

Was the 'discover' doing that on that large a profile or in general?

I secured
it in that case with a few layers of PVC tape as it does not see much
pressure, and small leaks wouldn't matter. I suspect if you used a
jubilee clip, especially when it was warm, it would be very effective.

Or a few turns of galvanised garden wire twisted up at the end?

https://www.machinemart.co.uk/p/3in-reinforced-hose/

Yeah, that sort of construction pipe is often used on boats and in
caravans (for waste / bilge pumps, where I have sometime used the
warming trick).

Cheers, T i m