Shooting opiates is WAY different than taking them orally, I'm 99% sure the standard dose of Dihydrocodeine is 30-60 mg every 4 hours.
That being said, I'll only be trying double the standard dose as a test so 120mg, maybe even 90mg. I know you can get 120mg extended release DHC so I don't think it's too unsafe taking 120mg first time, plus I'm opiate experienced. And I've read a lot that people have took over 1000mg of the stuff and lived.
If I do decide to take them rectally I'll probably only do 30mg and MAYBE another 30mg 1 hour or so on if not feeling much.
Prepping things for rectal administration is very simple. The extended release mechanism for pills like Dihydrocodeine are by no means as sophisticated as those for drugs like Oxycontin or MsContin. They typically just consist of a "softer" portion of pill to dissolve immediately and a "harder" or more dense portion. You can typically crush these just like any other pill, although slightly more elbow grease may be required. A mortar and pestle isn't a bad investment anyway (5$), so I'd suggest getting one. It also provides you with a nice concave surface in which to mix and draw up your solution.
So, you basically just crush the pills up into a very fine powder. The powder must be fully soluted with the water, as you're rectum doesn't have the same ability as your stomach to break down and digest things. It can only asbsorb liquid. I usually use 10ml of water. You can use less with less material, but with large pills like this, you may need more. It just matters that you have a solution. Crush pills, mix with water, draw up, insert syringe one inch into rectum and slowly depress while lying on side or stomach.
The beauty of the ROA is that effects come on quite fast. You'll probably begin to feel effects within 2 minutes and will peak around 15-20. So if you want to titrate your dose, you don't have to wait an hour to do so. If you want, you could prepare your entire solution in advance, like as much as you think you might end up using, then all you would have to do is go back and draw up another few Ml's of solution.
I usually just lay on my stomach, inject and Bluelight on my tablet as I wait for the effects to come on. It should only take about 15 minutes or less for the entire solution to be absorbed as well, so while others choose to lay down for up to 45 minuts, I've never found it necessary. Whatever works for you.