Connecting 2 water tanks?

[StephenStephen]

I have a water butt and a large rectangular water tank. I've had them connected together with a (slightly random) 15mm speedfit arrangement.

I want to upgrade it to a wider bore connection with a flexible pipe.

It's not possible to get to the inside of the big rectangular tank, but I think the walls are thick enough to screw a connector securely into.
I'm thinking to drill a bigger hole then use a brass screw-in fitting with ptfe, or with some kind of waterproof sealant?
The water butt I can (though it's a stretch) get to the inside (if I hold the nut on an adjustable wrench).

I'd be really grateful if anyone can suggest how to find the brass fitting, pipe and fitting at the other end, that will play nicely with each other.

Thanks for reading, and any thoughts or suggestions, Stephen

 

[HERTS P&D]

This might work with extra fittings to connect to your pipe.

https://www.amazon.co.uk/GARDENA-Push-in-Tank-Connector/dp/B0DMFB1R73/ref=asc_df_B0DMFB1R73?mcid=761d6f7b50743f3d9083b13b96a5dcf5&th=1&psc=1&tag=googshopuk-21&linkCode=df0&hvadid=787352598229&hvpos=&hvnetw=g&hvrand=6331410256678179243&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=1006625&hvtargid=pla-2398806087582&psc=1&hvocijid=6331410256678179243-B0DMFB1R73-&hvexpln=0&gad_source=1

Andy

 

[Mottie]

This is how I’ve connected mine up over the allotment. Not my actual butts but the same system.

 

[CountryFan]

What is the rectangular tank then? Any photos/web links?

 

[StephenOak]

What is the rectangular tank then

Probably an IBC

Intermediate bulk container - Wikipedia

en.wikipedia.org

The hole (middle of the top) is c. 8" in diameter, so fine for getting the contents in/out, but no where nearly enough space to reach in and secure the inside of a fitting.

A neighbour has some at the bottom of his garden and pumps water from his water butt into them, so he has plenty of water for his plants.

AFAIUI some are only used once (or a small number of times) are are then disposed of, so they are relatively cheap.

 

[StephenStephen]

What is the rectangular tank then? Any photos/web links?

I bought it from the dump a few years ago, I can take photos in the morning