oh god!!!!!!!
this is one thing i know way too much about
first. NO PVC!!! i dont care what you read where! butane is an oil byproduct as long as thats true i dont want my extraction tube being any type of plastic.
you want a higher yeild? then you want a smaller tube.
do more runs with 8th to 1/4 oz tops in a GLASS tube!
thats all you can do for yeild, for quality you need a 2 stage vac pump rated to -31g at a 15 micron rating.
not cheap. and thats not all you need. but it will get you way above average.
theres a lot that goes into it, i posted an entire detailed tek in the concentrates thread, check it out.