You should clean their tank or cage about once a month. First take out all the accessories. The old bedding should be thrown away but keep about a cup of the old bedding for scent recognition. Next scrub the tank with non-toxic soap and rinse it thoroughly with water. You should do the same with the accessories. Put fresh bedding and all the accessories back in the cage. Finally, put your gerbils and the small amount of bedding back in. They should look very excited if you did it right.
Holding your gerbils is vitally important and the highlight of gerbil care. Holding your gerbils helps gain their trust and keeps them tame. Before you hold your gerbils, wash your hand to prevent them from biting. When you hold your gerbils talk to them softly and when they hold still, that's a sign that you can pet them. When you put them back make sure you give them a treat. Oats and sunflower seeds are good examples. Make sure to wash your hands again after.
You may have noticed that I have been using the term gerbils instead of just gerbil. That's because gerbils are social creatures, they live in pairs. If given a big enough cage male gerbils can sometimes be held in groups of 3. If you want to ensure the happiness of your gerbil you should get him or her a partner the same gender unless you want pups. If you have a lone gerbil you can request a single gerbil instead of a pair.
It's not just the tank you have to give a bath to.
Gerbils need them too, but instead of water they use sand to clean themselves. Put sand and/or corn starch into a bowl or jar, then put it inside their tank. Watch them. When they start to look lighter than their usual coat color take the bath out. You should give your gerbils a dust bath monthly like the cage.
One of the main reasons gerbils die early is because of poor cage placement. When you place a cage make sure it's indoor and not near any air fresheners, vents or sitting in direct sunlight.
Hideouts aren't in the needs list but it should be. Gerbils need a place they can feel safe so the can sleep, eat, groom, and well hide. You can find MANY different kinds of hideouts at pet stores and online but you can also just give the gerbils a cardboard box with a hole in it and they will make it their own. Even though you gave the gerbils a cardboard box to chew it's still good to give them something else to chew for some enrichment every other day.