inline diesel fuel heater

i have just aquired a second hand inline diesel fuel heater

for my 300tdi disco it has two inlets and outlets. The electric parts

are not a problem (sparky by trade) but i was wondering about the

plumbing its my intention to run the pre main filter pipe through the first

part and the post filter pipe through the second part. Has anyone got

any experience with these and are there any pitfalls

i have been running on biodiesel untill recently and hope to use the

heater to allow me to run bio through the winter

thanks Mike