a code compliant method is to use a trap primer setup. These are installed on all new/remodel floor drains. They can be piped from another fixtures tailpiece, toilet bowl or a special valve connected to the CW piping. I suggest google "trap primer".
Here is a link to a waterless primer system. Never used it but it might be good for an existing floor drain
http://energizecorp.com/products-page-2/sure-seal/sure-seal-waterless-floor-drain-trap-sealer/
Here is a link to a waterless primer system. Never used it but it might be good for an existing floor drain
http://energizecorp.com/products-page-2/sure-seal/sure-seal-waterless-floor-drain-trap-sealer/