I IV MPH on a somewhat regular basis, I find what's great is that I get a rush and, albeit much less euphoric than IV coke, I don't have the horrible cravings that I do after even a few shots of coke
I've had AD/HD since prior to age seven and used to take Adderall (mixed amphetamine salts). I hated the ups and downs. That and the fact that I'm a user, I choose to go the non-stimulant route, taking above the "max dose" (based on children) of Strattera (atomoxetine, the only "FDA approved" non-stimulant AD/HD med). I got about 30% symptom mitigation, at least at first. After 7 years it quit working completely, so now I take it with Vyvance (lisdexamphetamine, MUCH better and much smoother than Adderall IR).
Prior to getting scripted Vyvance, my tolerance was low and I could get a nice rush off five 10mg blistered Novartis Ritalin pills- btw, I mean a rather INTENSE rush, if you have no tolerance, PLEASE don't use my usage as a guidline of any sort, I tend to require/want large amounts of all drugs
I simply break each pill into fourths and backload it into a 3ml syringe (sans the needle)- then, I insert the plunger, get the water nice and hot, and fill the syringe to the 2ml mark (holding it upright of course). Although the solution goes to the 2ml mark, I pull the syringe to the 3ml mark- that "extra" 1ml of air allows for more vigorous, effective shaking. I shake it for a mere 30 seconds or so, then fill it to capacity and shake a little more. I like this method as it avoids having to crush the pills (more opportunity for unsterile conditions) and it completely dissolves the pills
Note that the solution is CLOUDY and MILKY at 50mg in 3ml

... you think you'll have to pre-filter with cottons, then use 2 different sizes of micron-filters. However, filtering it through a single Jumbo cotton ball packed in a 12ml syringe produces a solution that looks like water

I'm not saying NOT to use a micron filter, simply that I'm surprised such a milky solution filters out so well with cotton- crystal clear
Anyway, you'll of course have less than 3ml after filtering. Now, I'm on bupe maintenance; however, I've discovered I can continue taking my bupe and STILL GET HIGH on pentazocine (I have a thread on IV pentazocine and bupe). I've found I don't like the actual high all that much (that is, 50mg IV pent or so); however, I love the rush... I only need 10 or perhaps 20mg pent to greatly intensify the rush of the methylphenidate
So, since I have less than 3ml of solution, I basically repeat the above except with less water and using pent instead of MPH. I then mix this with the MPH in a new, sterile 3ml syringe, add a Luer Lok tip, and it's off to the races %)
EDIT: I HAVE shot MPH using only a 1ml syringe- however, the most I've put in there (and still gotten a clear solution after one pass through compacted cotton) is two 10mg pills.