Once you have your drawing needle loaded pull the plunger out of the slin and slowly push your oil in to the slin. Go just slow enough so that your oil runs down to the tip of the needle. Go to fast and the oil gets caught part way down. Touch the plunger to the back of the slin barrel with just enough pressure so your not pushing anything out the needle.
Slowly tip the needle allowing the air bubble to make its way to the tip of the needle. Push out as much air as possible and you'll still have a tiny tiny bubble in there so point the needle down an flick the hell out of the barrel to get the bubble to be against the plunger. Good to go. It seems easy to me cuz it what I've always done but I can see it being a but more difficult with something like t400 but still shouldn't be that bad.
Obviously it's slower then injecting with a bigger needle because of the whole process but if it's gonna save you building scare tissue why not. Said and done it takes me all of five minutes to complete the injection so I wouldn't a to bad.
Also up I'm not sure what brand of slin pins you have access to but up here in Canada the best brand to use is by far UltiCare