I use a lot of extract and process it myslef into pure using chromatography and steam distillation among other techniques. Obviously very little extract is valuable and inevitably I end up with glassware that has good extract coating the insides after I pour the rest out. Some glass is very hard to scrape out due to geometry like a flask.
Method one is pretty good and does not use solvent - I use silicon baking mats from Amazon. They are a joy to bake with because nothing sticks to them and they take heat up to about 350 F for baking. In the past, I placed the glassware upside down on a silicon mat in the oven and turn it on to 250F or 300 F. By the time the oven is heated to that temp the extract will have run out and onto the flat baking matt. Recovery is pretty close to 100%.
The other more thorough method involves solvent and is the method I use.
Any solvent will do although some pose a little different problem when purging the solvent. I have used, hexane, acetone, isoproply alcohol, ethyl acetate, and methanol across my processes (chromatography) and any one of those is safe to use as a solvent to clean your glassware although fire safety must be observed. MSDS sheets are available for each and should be read and understood.
Labs generally prefer acetone as the polarity is right in the middle of the charts and it does a damn good job at cleaning. It is available as pure acetone sold as nail polish remover. It is cheap and evaporates easily and is not particularly toxic to the little girls cleaning their fingernails wih it.
If you pick/use any alcohol other than methanol the minor problem of purging water arises because all alcohols except methanol form an "azeotrope" with water which means that once water and alcohol mix (except methanol) then you cannot seperate the two by boiling.
Now, a word on purging. At most for each gram of material you intend to disolve you need 1 to 2 milliliters of solvent to make extract liquid. Add another 10 ml so it flows smothly and at most you are looking at 10-15 ml. No solvent should every be ingested but frankly the body will gag if you attempt it. Medically speaking most solvents would not kill a person who accidentally ingested 15 milliliters of any of the listed solvents. So the issue of purging is one of making it vapable again more than an issue of eliminating poisoning potential. Extract will impart a nasty flavor when traces of any solvent are not purged and it will make you cough (the body naturally purges toxins immediately), which is undesirable but not deadly or really harmfull in the dosage you would inhale in a vapor hit. It is simply uncomfortable and tastes bad.
I place the solvent with extract into a low ceramic dish. Ceramic is better than glass to do this because ceramic will not break if heated on stove top. They sell perfect sized ceramic dishes at Petco for a few bucks in the isle that sells stuff for rodents (watering dish). I place on stove top and set temp halfway between medium and low which is not enough to boil water in a pot but almost given enough time. Then I stir continuously while heating until all visible bubbling stops. At this point if you have a vac chamber ($100 from shattervac for chamber, $200 for a decent dual vane vacuum pump) then pop it into chamber and pull hardest vac. Then back out of chamber and back on heat to repeat four times.
In the circumstance when you do not have a vac chamber it is still easy but takes a bit of patience. After the bubbling stops, instead of a vac chamber set the hot extract aside for one hour or more at least. Then back onto the stove, heating and stirring again until the oil is very hot. Off to cool again for an hour at least. Repeat four times. Either procedure will completely purge the extract of solvent and after four times you should see zero bubbling after the extract is heated very hot.
With alcohols, water will get left behind and this too can be heated and stirred away, however, water is heavier than extract and lays underneath of it in a dish. If you do not CONSTANTLY stir the mix while heated then the water can and will turn to steam underneath the oil and "pop" through which makes a mess.
Lastly this item is a bit off topic but relevent. I do not use ethanol for good legal reason. First, ethanol is unreasonably expensive owing to the huge tax placed on drinking alcohol. Secondly, because ethanol is regulated by the folks at Alcohol, Tobacco, and Firearms (ATF), the distillation of it even if it is to recover the solvent is generally a felony crime in most states unless licensed to distill ethanol. The exception is if you immediately denature the alcohol by poisoning it with some other chemical, as they allow for biofuel production at home.
Furthemore, because arguably it is not a poison per se, then any extract disolved in it could be considered by law enforecement to be drinkable cannabis product. In Oregon the law imposes strict limits in the amount of consumables allowed and the potency therin PLUS if you are not licensed to produce drinkables it can also be a crime (the law is absurd). So any up and coming law enforcement guy that wants to be a prick could in theory "pop" a person in a variety of ways if extract is disolved in ethanol. HOWEVER, there is no law I am aware of that makes it illegal to posess acetone, methanol, or any of the rest of the solvents with extract disolved inside. In this form it is a poison and any misguided law enforcement effort would have a tremendous legal burden of somehow proving acetone with extract in it was a usable cannabis product. Same with methanol. I would even venture so far as to say that hypothetically even several pounds of extract would not be illegal if it is rendered temporarily poisonous like they do with ethanol (called denatured alcohol to render it undrinkable).
