-Remove the fuel tank - yes.
-To replace the diaphragm only, no need to remove the petcock or drain fuel.
Just roll the tank forward onto its front end (on a towel), and you can work on it just fine.
-To change the fuel strainer, remove the petcock from the tank, still no need to totally drain the fuel.
Note, draining the fuel primarily makes the removal and reinstallation of the tank much easier.
Hope this helps
