Please describe your application in more detail.Type of transmitter:Bubble tube,open tank,closed tank,electronic output,pneumatic output, etc.

this is for pressurised vessel,elecyronic o/p.

Once the lines are bled of all air(assuming liquid in lines) there will be no flow,so pressure drop in the line will be minimal.One line above max. liquid level, and one at bottom of vessel.Electronic output (4-20 milliamp) doesn't care about length very much, unless the wire resistance is very high.Put the transmitter as near as practical and try to eliminate any air pockets or traps in the lines.You must also allow for the heigth difference between the transmitter and bottom of tank.

Hope this helps