I don’t bother cutting the dip tube. I just blow out the sediment in the bottom before either serving or xferring to a serving keg.
I cut my dip tubes quite generously. So much that I’m leaving about a pint behind when. Tranfer to a serving keg. The reasoning is that I want to minimize the sediment that gets into the serving keg. In particular the last pint will be cloudy if you don’t cut the dip tube since the beer level has reached the domed bottom and starts washing sediments off its slope. But if you are serving from the secondary you may not care.
Kai
Count me in a as a dip tube cutter as well (I have 4 or 5 cornies with shortened tubes used for bright tanks). Though, on beers I am not particularly concerned about clarity with I don’t bother using a bright tank (or secondary for that matter) and just blow the first couple of pints as cloudy, Of course, I drink 'em. Its good for you. 
Well, maybe I’ll just have to try using my cornies as fermenters then. I guess I can see where cutting the dip tube might be nice for saving yeast if I used as a primary fermentation. But sometimes I get a lot of sediment so that worries me. Sorry for getting the thread off track. :-[ :-* 
+1 here
After reading the posts and seeing as I have 10 cornies, I’m gonna stick my neck out and cut two dip tubes and use those cornies for primary and use two uncut for secondary fermenters. I’ll keep my carboys handy though so if I don’t like it I can fall back on them. 
I transferred my Kolsch to a secondary better bottle yesterday morning to my 35F chest freezer. It’s been about 36 hours and there hasn’t been any airlock activity other then some positive pressure. There isn’t any headspace and it started at 65F.
You can use tubing cutter for it.
I would cut only 1/2 inch to begin with.
I have two kegs with dip tube cut off and I use them as clearing tank (I rack beer from fermenter here first).
I see you are going to use it in different manner.
This is late, but I just had a lightbulb moment!!!
next time I do this I’m going to have a hose coming out of my airlock (like a skinny blowoff tube) thats connected to some kind of variable volume bag. The bag will be filled with CO2, and allow co2 exchange in and out of the fermenter. right now for a bag i’m thinking that a wine bladder might work well. also those collapsable cube containers that some of the online HB store sells might work.