In theory you can crush and rinse as many as your want. I just find it easier to work with small amounts since the leftover binders seem to hold onto a good portion of the water.
There's no real way to do multiple shots at once without using two iv sites simultaneously. What you can do is get a bigger barreled syringe, or evaporate off some of the extra water in the solution. This is normally what I do when prepping these pills for iv use. I typically use 10 pills - do in two groups of 5, and two rinses per group. This leaves me with a lot of water. I put it in something like a big soup spoon and with as little heat as possible, evaporate off some water. Don't let it bubble or get to a boil. I don't know off the top of my head what temp oxy begins to degrade at, and I can't swear that evaporating water won't cause a small loss of product. But it has worked fine for me. I also didn't realize what a difference saline solution makes to how I feel after a shot. This is tricky if you're going to evaporate off liquid because you don't want to boost the salinity too much. I usually use 1/2 or 1/3 saline, then the rest water, if I'm planning on evaporating water off of the solution. If you just want to shoot it without evaporating then saline is definitely the way to go.
If you are using an isotonic saline solution then in theory you can inject any amount of volume because it will not effect the salinity of your blood or mess up your electrolytes. The only issue here is a large volume of solution can be harsh on the iv site and you need to take it very slowly. And to answer your question - always release the tourniquet BEFORE shooting. You tie the tourni, find a vein, hit it and register with your rig, then release the tourni, reflag to make sure you're still in, and inject slowly and steadily.
I'm sorry to hear you have chronic pain, I go through that as well (albeit untreated at this moment). There are several other opioid available. The benefit to the oxy you are currently getting is that you're not stuck using the needle if you don't want to. The oral BA is very high so you won't be "wasting" any if you're in a situation where banging them isn't an option. Drugs like hydromorphone, oxymorphone, and morphine can all be prepped for iv (if you have IR formulations) but have very low oral BAs. Hydromorphone is notorious for the rush it provides but also the short duration. Most drugs have a short half-life when injected. Any of those would be suitable for IR breakthrough pain as well as iv use. However...I don't know if any of them will last longer than iv oxycodone though, I'm sorry. Do you take an extended release painkiller too? Hydro/oxymorphone and morphine are known for their rushes during iv, but do you really want to set yourself up so taking them as scripted is no longer an option? I would stick to the oxy so you have all other ROA available. If you are scripted so many, would your doc be willing to give you IR 15mg or 30mg tablets instead? These would be MUCH easier for iv use.
I do have to say that if you plan to continue shooting pills long term, please look into micron filters! They are available online and totally legal. You do need leur lock syringes to use with them, but ordering these would allow you to be able to get a large barrel syringe and a small gague needle since it's sounding like you have a lot of solution to inject. You can also get sterile water, saline solution, sterile vials, bacteriostatic water, etc etc etc. Check out the micron mega thread:
http://www.bluelight.ru/vb/threads/481622-Micron-Filtering-Mega-Thread-and-FAQ
PS Sorry all my replies have been so long! I'm just trying to explain the best I can.
and as regrettable as it is I never have been able to get my hands on dilaudid but I hear it is epic. Have you tried? Something also that may shock you a friend of mine told me that he was iv sub strips and at first I was like fuck that. But honestly its really actually not bad. Not sure if you are in US or EU buy suboxone strips about 2 or 3mg is kind of nice....no rush but a kind of speedy weird energy high....nice with morning coffee
