OR you could be crafty and just save the bongwater(so long as it has zero adulterants itself such as sugar, or flavoring), and you can actually just throw it on a plate or in a pyrex dish with a flat bottom, and microwave the liquid until the water evaps off of it, and then either scrape the resulting residue with a razor blade if it's flat-bottom plate, or i just take a credit card and scrape it really hard against whatever plate/dish i'm using, because the card conforms to the shape and curvature. then you can just throw it back in bowl after you've collected everything. be careful tho, these resulting goods are quite potent. also as a side note: in its liquid form i've kept bongwater that had meth dissolved in it for as long as 4 or 5 months, in a small jar. and it'll keep perfectly fine without souring or anything so long as there is no sugar or flavoring or colorants present. makes for quite a rainy day fund
also, you'll wanna stick to smaller rigs/mini dab rigs for this. the larger the piece the more wasteful it feels in terms of your initial product