Regards " Syphoning ", What this site has long since taught me to do is to buy a meter of the right sized plastic hose to fit over the tap at the base of my FV's. Slip the hose onto the tap. Poke the other end, as Arturobandini says, to the bottom of ye keg. (Obviously, for this we have the FV elevated above the keg). Open that tap.
This is a great advance on sucking about with thin bits of pipe, like we used to do. I remember spending many an arm deadening hour, holding a wretched 1/4" diameter length of tube as the beer piddled out

Now it's just crack, gush, done
Mould in ye keg? Strong, hot solution of Soda Crystals and a cloth. Pop the cloth in. Pour in a pint or two of soda solution. Cap on and shake the hell out of it. That'll shift the mould.
Then sanitise as normal.