New Siphon for Old Cistern?

[The Jeep]

Hello folks, well it's been many years since I posted here.... I've had a look at similar posts, but can't find anything on the exact issue that I have, so here goes:

I have an old Shanks low-level cistern and I need a new siphon to go inside it. The bottom hole is 2 1/2 inches in diameter and I've tried with the largest Dudley siphon that the plumbing shop had and I was told that it should fit. However, it doesn't... after days of trying different levels of silicone and none at all, it doesn't hold any water pressure and leaks with half an inch of water in the cistern. The rubber seal is simply too small and only covers the hole by about 3mm at there narrowest point.

So, is it just not possible to find a suitable siphon for an old cistern? Or does someone out there know better? If so, I'd very much like to hear from you!

 

[Exedon]

Some sort of a large washer required back in day would have made one out of lead.
I,m lucky enough to have a mate who has a metal bashing shop I would have a couple of stainless steel washers made.

 

[Nige F]

Have a look at LUNNS plumbing supplies on t'net

 

[CBW]

Try these or perhaps a cable siphon with a 2” outlet?

 

[JimCrow]

 

[The Jeep]

Thanks guys, I went for the Lunn's adapter solution before seeing the Toolstation one, but I'm sure it will do nicely - thanks again