Once left one of mine in the van for weeks and it started to come to life. 
What i do to clean the tube is tie half a cotton wool ball in the middle of a longh length of twine, then feed the twine through the tube, (i use a length of curtain wire to pull it through) secure both ends to something then "walk" the tube backwards and forward to clean the whole length.
I'll also soak it in milton again after just to be safe.
This is how i i've always cleaned mine and i'm still here.
Include a little history in your walks. Pecsaetan - Ancient Derbyshire, Staffordshire and South Yorkshire - http://pecsaetan.weebly.com/