casting gel in the gel tray
I checked the dimensions of the gel tray in the Instructible files you published and the tray seems to be 7x7 cm interior size. The width of the tank is about 7.5 cm based on the same files. Normally the gel is cast by turning the tray 90 degrees but if we do this with the current design we get a gap of about .5 cm so any gel we poor will leak in the tank before solidifying. How do you cast the gel
So, with our gel trays, you use tape to close the ends of the tray. Most kinds of tape will work, just make sure you place tape over both ends and that it covers the edges well so it won't leak. You can test with some water if you want to check before pouring the agarose. Once the gel has set you can peel off the tape.