Question over pipe work return pomp ??

[Jason mack]

hello folks ,
Should my return pipe from sump too tank be 25 mm or 32 mm ?? Ive Never done a sump before .. :oops:

 

[Jason mack]

hello folks ,
Should my return pipe from sump too tank be 25 mm or 32 mm ?? Ive Never done a sump before .. :oops:

Or even 20 mm ????