Naptha isn't nearly as volatile or offensive smelling as other solvents. Heptane is even less offensive if you can use that. As long as you keep some windows open and maybe a fan going, you should be okay. Naptha is used for a lot of stuff, from bbq to lighter fluid to getting goo from stickers off of stuff. Your neighbors probably won't even notice the smell coming out of your widows, but they may see you doing something that they consider strange if you do it outside.
Another thing to consider is that you are using the q21q21 tek, which is fast, efficient and provides good yields, so you won't be doing it very often. A lot of people get over 1.5% yields with it, so if you extract from 100grams of mhrb, you could get ~1.5 grams. Which should last you quite awhile. So, don't worry, your neighbors won't think you are running a meth lab.
I wouldn't do a hot water bath with a sealed jar, because pressure could build and you could end up with a mess. You can pour the initial pull off after as little as 15 minutes, so you won't have super long exposure. Naptha really isn't that bad, compared to the nastiness of xylene.
Good ventilation and no open flames or smoking. And no heating over open flame or active electric elements. Just remember that and you'll be okay.
Let us know how things go.
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