try this

draw the curve an snap the circle to the start of it
select both go animate -> motion paths -> attach to motion path

in channel box change eith side, front or up twinst under motion path1 to 90 so that it is perpendicular
select the circle go animate -> create animation snapshot options chose increments of 1 (the more u have the better so u may need to exp with this value) an chose timeslider
click apply

u should have a series of circles that follow the curve select the circles an NOT the curve and go surfaces -> loft

an u should have ur tube

good luck an ask more if u get stuck with this