If you search I think there is a methadone syrup extraction tek on reddit. Can't vouch for it myself though.
I used to inject the methadone oral syrup quite abit. A really horrible practice, and as others have mentioned, the concentration it comes in isn't a sufficient strength to produce a rush due to the large amount of liquid, especially if you are highly tolerant. Since my oral daily dose was 380mg/day, the amount of liquid required was significant. I don't believe i ever tried to shoot an entire dose of 380mg. The stuff burned quite abit when injected.
When I shattered my ankle in a very gruesome way I had to have surgery whereby they attempted to piece it all together.
Since 380mg of methadone was my daily baseline just to feel normal, the morphine drip they gave me did absolutely nothing so my clinic told them to give me my methadone dose intravenously.
The methadone shots they gave me got me higher than I've ever been on methadone. I was actually getting worried because i was nodding so hard and uncontrollably and had to really concentrate on my breathing, as if I had to focus on each breath. I almost told them that it was too strong, but the junky in me decided to roll the dice since I figured if i was going to OD at least I was in a hospital. It sort of made me wonder if the oral methadone I was getting from my clinic was less than what they had been leading on.
Unfortunately when I got discharged from the hospital I was in for a rude awakening, because even though they increased my oral dose to over 400mg for a few weeks, it didn't seem to touch the pain really.