How can I waterproof this?

[mothhawk]

I like the idea of putting the tube in a pop bottle - I'll have to hang around the recycling point in the village... don't drink fizzys.

[out in the cold]

Are you a hillwalker?

Nikwax can be used to waterproof paper, so should work on cardboard.

Problem is, it is mighty expensive to be using like that

[mothhawk]

I like the idea of putting the tube in a pop bottle - I'll have to hang around the recycling point in the village... don't drink fizzys.

[marchogaeth]

I like the idea of putting the tube in a pop bottle - I'll have to hang around the recycling point in the village... don't drink fizzys.

A bottle of water? Or ask at work? Cafe/restaurant? (I use empty 2l plastic bottles for watering.)

[mothhawk]

I buy bottled water occasionally (I find I can leave it in the car for weeks if necessary without the water turning green, unlike tap water), but the bottles have a "waist", too narrow for the tube.