These air tubes are made for the Marchisio Variable Capacity tanks.  Please choose your size based on the chart below:

400 air tube fits (40cm):
80L Flat Bottom Tanks
100L Flat Bottom "Tall" Tanks

500 air tube fits (50cm):
100L Flat Bottom "Squat" Tanks
200L Flat Bottom "Tall" Tanks

650 air tube fits (65cm):
200L Flat Bottom "Squat" Tanks
250L Flat Bottom Tanks
300L & 400L Flat Bottom Tanks
300L & 400L Conical Tanks

800 air tube fits (80cm):
500L-700L Flat Bottom Tanks
500L-700L Conical Tanks

900 air tube fits (90cm):
800L-900L Flat Bottom Tanks
800L-900L Conical Tanks

1000 air tube fits (100cm):
1000L Flat Bottom Tanks
1000L Conical Tanks

Some sizes may not be listed.  Give us a call at (510) 849-0400 if you have any questions!