My suggestion, buy yourself a Nammor Hose or the washable hose from hookah-shisha.com pictured here: http://www.hookah-shisha.com/store/p...&idproduct=486
Sambooka uses this hose mainly, and he says it doesn't taste like plastic and it doesn't retain any smell or flavor. It's also real cheap at just $8.00 If you go for the Nammor, be prepared to have a plastic taste ruin your sessions for the first 6 or more times. I recently bought a Nammor, and I couldn't get the plastic taste out of it until after a week of smoking. I, like you, tried lemon juice w/baking soda, even vinegar, and yet nothing took the smell and taste of plastic out.
I had to just wait it out and "break it in". Try rubbing alcohol though. That might actually work. The other day I was trying to get this rancid smell out of my hookah. Baking soda wasn't cutting it, neither was vinegar. But I decided to try rubbing alcohol, and it actually took the smell out completely. It worked wonders, and now my hookahs smells new again.