Hi David, just been brousing and came across your Drains.
I too have a stumbling block of John Drain abt 1850, supposedly born in Pollockshaws, but can find no record of him. Anyway, his Father was a Henry mother Jane McClellan.
They had most of their children in Ireland [County Down] found some of their births and all of thier marriages, most of which took place in Glasgow. The above Henry's father was also a Henry and mother also a Jane Wilson or Watson. My point is I've got a few Drain going back to 1820, if you would like to email me some of your details I'll see if any link to mine.