Yah, gear went in then added water, or at least that's how I would see majority of past guys do with me.
Dude ---- make a solution in a separate container (meth+clean water),
FILTER THE SOLUTION then put into syringe.
Don't assume that everything in "shard" is pure/water/soluble/clean. You need to extract insoluble particles. They may not be visible to the naked eye, but can cause innumerable problems.
Putting things into a barrel before filtering in means it is no longer sterile or safe to use.
As for dexamphetamine (etc) for "maintenance" style addiction treatment; I only think it could make people worse. You're still taking amphetamine, with all the problems that go along with that. Unlike say opiate maintenance, where the biggest physical dangers lie in fatal OD and such (but pose fewer toxicity issues) and help the addict stay functional (out of withdrawal) - quitting speed takes willpower and lifestyle changes.
There have been attempts at replacement therapy for meth, but I think the Opiate maintenance model doesn't fit the pharmacological profile of methamphetamine at all.
Maybe some day....but amphetamine is amphetamine - risks of psychosis and such are still highly present.
Not to say that medical options shouldn't be explored - but on a personal level, I'd try something else to get my kicks.
Exercise, study, art....psychedelics (if you must take drugs).
Dexies for meth addicts should only be considered case-by-case IMO.