What recipe are you following?
Typically I steam mine then pour off any excess liquid. I will add my fat of choice -butter, bacon fat, even coconut oil then use my immersion blender to get a mashed potato style consistency. If you are using a masher (probably not the correct terminology for the kitchen tool, but I think you know what I mean) you may be releasing extra liquid as you mash.
Maybe hold off on adding your fat, mash - drain, mash -drain, repeat til the extra liquid is gone then add your fat and mash a little more.