Some people find it may take a few goes to get used to the feeling codeine gives you, just from a HR point, I would try like ~5times before upping/adding other drugs into the mix,
I used to get the warm opiate euphoria off one pack of Panadeine Extra (360mg) for a long time, then I started getting offered 600mg when they came out and my tolerance skyrocketed, and now codeine is worthless at doses lower than 800mg and chemist hopping sucks. I didn't just jump in the deep end so to speak, is all I'm trying to preach.
Phenergan should be taken about 45min to an hour after dosing or it will lessen the high. Valium is a CNS depressant like codeine (and to a lesser extent Phenergan I believe) so be careful, i don't know what your tolerance is like.
With that out the way, if you still have no luck you could be a poor metabolizer, I would dose 100mg more each time after the initial 5 tries, but if you get to 600mg and still a no go maybe try PST? Indybreaker was in your situation, read a few pages back
I would definitely smoke cones before during and after, it always enhances the warmth/euphoria and helps prolong it.
[Can anyone shed any light in this one?] "Dextromethorphan is commonly available as the monohydrated hydrobromide salt, however some newer extended-release formulations contain dextromethorphan bound to an ion exchange resin based on polystyrene sulfonic acid. Dextromethorphan's specific rotation in water is +27.6° (20 °C, Sodium D-line).[citation needed]"
Back when I used to use DXM it came in a blue box, you want the one that has DXM hydrobromide as the only active ingredient, some come with Guannifesen (sp?) that is a deterrent to stop people from abusing it. I dont know if its still the one that contains only DXM so double check but heres what it looked like
edit:removed pic, see below
Im not too sure about dosage of DXM to potentiate codeine, I have sworn off that stuff a long time ago, before I started codeine. You want to take just enough to not overpower the codeine and ruin the opiate buzz.