a friend of mine has a red eared slider...

That thing'll need a baby pool form wal-mart. Complete with rocks and sun, they like taking a tan. But to keep him indoors, heat lamp, filter, I raised turtle on turtle pellets, eventually he'll be eating feeder fish. He'll need a landing. Watch out a happy turtle will grow fast. I personally will not keep turtles in the house anymore. They stink badly. Lots of bio. Filters are a must. Oh and they live a long time and get big. Happy

Sliders are basking turtles and spend many hours a day, well....basking! They need an area to come out of the water so they can completely dry or they can develop skin fungus. A basking spot of about 90˚ is important as is a UVB source. The water temp should be close to 80˚ for a baby.

Sliders grow fast so if your friend wants a cheap up grade, he can use a rubbermaid tub. But in the end a pond is the best choice. For food you can feed a varied diet of turtle pellets, cichlid pellets, worms, crickets, freeze-dried shrimp, frozen fish and prawns, bloodworms, snails, aquatic insect larva and as the turtle gets older, leafy greens. Avoid goldfish feeders, they're nothing but junk food. I always have live Anacharis in with my turtles so they can nibble on it when they want to. Turtles are very messy animals so a powerful filtration system is a must.

Yeah, sounds like a nightmare! Turtles in general need a lot of care if they are going to be kept happy and healthy indoors in an aquarium. It's a shame they're so cheap and easy to find. Many impulse buyers never get them to live past a few months. Below is a link to a great care sheet for RES.

http://www.austinsturtlepage.com/Care/caresheet-red_ear_slider.htm

I've always kept my larger species of native turtles outdoors all year or most of the year. The thrive best in these conditions. Best of luck convicing him to build a pond!