According to google translate (I know) both are fine... Pidyn is the most common word Also acceptable, apparently: bidyn bidlen penis bidynnau cal cala caliau chal chala chaliau gal Consider yourselves fully versed in welsh gentlemen sausages.
The Bruce Griffiths Welsh Academy DICtionary says, among other things: pidyn (nau) cala (caliau) gwialen (as in 'rod) piden pisyn bidi coes (leg!)
The committee for making Welsh words out of English ones seems to have got really confused on that one.