Tubing from halfords £2.50
Cable ties- whatever you have already lying about
Syringe from eBay £1.50
Inject 10ml or so before going for a ride, remove the syringe and let gravity do its job!
Cheap as chips and works fine, I had a scottoiler dual injector lying about so used that, but you can put a bicycle spoke or similar in the tubing in order to get the correct angle onto the sprocket!
Only takes ten minutes or so to set the tube in the right place.