I've been mixing my own flavors, and initially had a standard 510-type atty for testing flavors. Yes, you do need to clean between flavors, and I then used flavorless (0-nic) liquid after cleaning to be sure all of the old flavor is gone. Some flavors seem to hang around even after several cleanings. I have one that I gave up on cleaning, and only use for menthol liquids, since I can still taste the menthol no matter how well I think I cleaned it.
Next, I tried an inexpensive rebuildable atty (
Phoenix Rebuildable Atomizer - Clone) Found this one easy to open up and rinse out nearly all of the old flavor. I like being able to see the coil/wick.
When I tried my first 'genesis-type' atty, with Stainless Steel Mesh, I took some of that mesh and made a vertical wick for my Phoenix clone. This combo is my current 'juice-testing' setup. Super easy to clean between flavors--just rinse under hot water and set wick/coil end down on absorbent paper-towel/napkin until dry. Most times, I'll vape one flavor until wick starts to taste dry, then top up with flavorless (all my DIY testing is 0-nic) and repeat with that until I cannot taste the first flavor any longer, or decide to rinse it out instead. When working on my DIY recipes, I'll taste 6 drops, then another 5-20 drops of flavorless, and repeat this for up to 10-15 times in an evening, or until my taste buds get overloaded (usually only get through 4 or 5 flavors).