Please ignore the above suggestion of taking 60 mg methadone with no tolerance. That's a great way to end up dead or in the ER. Ignore the trolling/ignorant/misguided Greenlighter.*
10-15 mg is a sensible dose to start with considering your oxy tolerance. If you don't have a daily habit, 10mg will probably work for you.
I'll echo other good advice offered in the thread: Do not dose again until at least 3 hours have passed since your first dose. Methadone is odd and some people can't even feel the come-up.
So that's my other point, for some people, Methadone does not give a traditional opiate come-up. It's more like all of a sudden (after 2+ hours) you realize that you're on a powerful but strange opiate. Some people actually feel it coming on. But in either case, methadone lasts a long time. Don't be surprised if you're feeling it a little the next day, even if you take 10 mg.
But since it takes so long to come on and since it doesn't feel at all like the warm, fuzzy onset of oxy, a lot of folks will re-dose too soon then end up nodding their heads off or ill as fuck 6 hours later. 'Done's a strange beast. But I hope you enjoy it. Be safe.
* btw, GL haden, using the word "usually" belies the no tolerance part of your post. And read the damn rules about Harm Reduction. Methadone's no joke and BL exists to keep people from dying/ODing. If you continue to post that kind of bullshit, I probably don't have to waste my time getting mad at your stupidity because you'll be gone before you turn Bluelighter. So I won't.