I have been successfully using my corny keg setup for about a year now but could do with some advice.
I use a Sodastream bottle instead of the conventional pub bottle and always swap to a new bottle each time I start a new keg. I am fine with the cost (£8 per swap) however I was wondering if anyone knew what would happen if I was to use it until it completely ran out as there is always a little left in there.
I was under the impression that as the pressure begins to drop from the bottle it would cause the beer to be drawn into the regulator?
After doing a bit of googling I believe I need a regulator with a “check valve” to stop this happening is this correct?
I have included a couple of photos of my rig below but as you will see the eBay listing doesn't mention anything about there being a check valve installed?
My regulator (well kind of... this is the photo of the one pictured in the eBay listing however the knob on the one i received looks slightly different. You get the idea though)
eBay item: 180889659970
http://www.ebay.co.uk/itm/180889659970? ... 26_rdc%3D1
My setup. (Since this photo was taken the masking tape has been replaced by 4 x velcro strips)

Is there a valve I can add to my existing setup to stop this happening and allow me to use 100% of each bottle without risking a pressure drop in the keg causing the lid to collapse, potentially spoiling the beer if I don’t pick up on it quick enough?
If anyone could help me out I would be really grateful.
Cheers Chris