How many liters is 3.75 kiloliters?

3750 litres

kilo means "multiples of one thousand", so just as a distance of 3.75 kilometres is 3750 metres, a volume of 3.75 kilolitres is 3750 litres.

But as the other poster said, it would not be common to use this unit for large volumes. "cubic metres" (often written as CBM) is more usual 3.75 CBM = 3750 litre