Connecting two pipes of different sizes

[ryanwatson]

I have a 12.5mm aquarium pump which I'm trying to connect to a 21.5mm pvc pipe. I can't find any connectors to do this job, anyone got any ideas?

I do need it to be water tight.

 

[Gerorge Standers]

Don't put PVC in an aquarium unless you want to poison the fish.

 

[ryanwatson]

Not planning to just have a spare pump, trying to connect it for a hydroponics setup

 

[dilalio]

To grow what exactly?

 

[DaveHerns]

He'll be asking how to bypass the meter next!