Hi, I have a blocked drain, have been trying to clear it using liquid drain unblocker but it keeps getting blocked up again, so I'm at the point of calling someone out to fix it but I know they're going to want to access the manhole. The house is a semi built in the mid sixties, I have a copy of the plan showing where the drains run, the drainage pipes are all on my side wall and the plan shows the drains running along the side path, but there's no evidence of a manhole. The survey I had done when I bought the house couldn't find one either. Is it possible for a house built in the sixties not to have a manhole?