Need help with sanke D coupler for fermenting

[reefriot]

So i know there are a few threads on this but couldnt find the answers or pics of what im wanting to know.
Since i started brewing 10g batches and have access to plenty of 50l sanke kegs i figured i try and use one for fermenting. Have a 10.5% Scotch ale rockin away right now just using a Orange carboy cap with blow off tube. While its doin fine i kinda wanted a easy way to rack. Saw a thread on using a D coupler for this and removing check valves.
So i like to ask questions twice and modify once so here goes.
The coupler i was going to modify is a micro matic and has the standard ball check on the liquid side. The gas side just has a rubber plug that sits in there. After removing both i still cant blow air out the gas in side. Is there something inside that needs to be removed?
My next question is about the spear. I have a few extras from my keggle conversions and want to cut one down so as to leave behind trub. How much do you cut off?
I dont want to waste to much beer but dont want to pickup any trub either. I can only guess a couple inches off would work but would rather ask somone doing this what the ideal length should be.
My last question would be are there any good mods for adding a air lock to the D coupler or just stick with a blow off tube for entire fermentation.

 

[wilserbrewer]

Is the lever handle in the down position? Gas will not flow at all in the up position.

 

[reefriot]

With the lever in the down posisiton i can blow in the gas in but cant blow out the gas in. Im assumming you would want co2 blow off to come out the gas in port while fermenting. If it tried to come out the liquid out port it would push beer up and out.

 

[wilserbrewer]

Hmmm, I thought there is just the gas check valve where the gas line attaches.

Does the gas travel outside the liquid out hole in the bottom of the tap? Contained by the large sealing washer.

Not sure if you are trying to blow back through the small center hole...sorry not sure.