Ear cleaning is only necessary when there is a build up of ear wax and dirt, or caused by ear mites (in which case, you see a fair bit irritated head shaking, scratching or even a head tilt). Most piggies have clean ears (although it is good to check regularly as it can be an indicator of a problem).
Please DO NOT attempt to clean the inside of piggy ears yourself. If you think this needs doing get the vet to check for any underlying problem such as mites. And ask the vet for a guidance on how to clean them and what to clean them with.