Just tried the lid of a 25ltr drum and it doesnt fit it has a different thread on it.
I have also just tried a 50mm pipe and that fitted but the fittings I was on about above are too small.
There is a place around by me that use these tanks, so I'll pop in there and ask them for the lids that come already fitted to the full tank, there must be a way we could make something for a lot less cost.
Hi Jeff. The lid on an IBC is about 9 inches accross!
This adaptor is for the base of the tank. No lid is fitted at the base as there is a tap there.
You have to trust me. These are the fittings you need and they cost £14+VAT+Delivery when I bought them.
The one on ebay looks home made to my eye. Also it is reducing the bore of the hose to 1/2" which is going to make your flow really slow for gravity feed.

I'm not on about the top of the tank I'm on about the bottom, when these tanks are delivered full, they come with a small lid/cap down on the tap section, these are normally thrown away when they begin to use the tank.
If you can get your hands on the lid/cap then you can make your own for less than a fiver. Trust me
I have a job to do tomorrow where they use IBC tanks, I'll ask about these caps and see if I can pick some up?
The one on ebay does look home made, but a tap as in the picture, fit it to the lid/cap hey preso your making a good profit as the taps you can buy from screwfix for less than a fiver, nice little proffit, he's making.