Just like portable washing machines, countertop dishwashers fill from a nearby faucet and drain into the sink. And just like with a full-size dishwasher the temperature of the water going in needs to be at least 120ºF to get good cleaning results. Most of these mini models have heaters to boost the temperature of the water for even better cleaning, rinsing, and drying performance and use about three gallons of water per cycle. Check the faucet connections included with any model to be sure you have the necessary parts to attach it to your faucet. Keep in mind they don't attach to faucets with pull-out sprayers.
Countertop dishwashers range in width from about 16 to 22 inches wide and 17 to almost 20 inches high, so be sure to take measurements before you buy so you know the model you've chosen will fit in the space between your countertop and upper cabinets. And capacities are small, so an oversized platter or a large pot likely won't fit inside. But most reviewers give them high praise for being real work and time savers.
All models have filters that require cleaning and some recommend a regular vinegar rinse to remove deposits and mineral build-up. While you shouldn't have to pre-rinse your dishes, it is a good idea to scrape or wipe off excess food before loading. And when it comes to choosing which detergent to use, packets, tablets, powders and gels are all fine in the countertop models. And while virtually all the machines have detergent and rinse aid dispensers that look and work like the usual ones, most brands caution against using packets or tablets for the short cycles as they may not fully dissolve.