I'd say that Galant has just about summed it up, Brian.

As I understand it, a MUG (terrible expression!) is a lower-body garment for men which consists of one leg 'tube' rather than the two of trousers!! Yes, Male Unbifurcated Garment.

As for "Tank", well I had never heard of this word being used to describe a kilt until I came to this forum! Where or how it originated I do not know, but I suppose it does conjure up an image of a traditional, heavy weight, woollen kilt - which is, I understand, precisely what it means.