The Glasgow life pools are generally quiet, I went to one in Garscube and there was just a few old people.
The Hilton and the Marriot just down the bottom of the M8 by the clyde both let people come in as a one off, check in with the time, my kid did water babies swimming lessons there so quite busy then but otherwise was quiet. I think most hotels do really, but those 2 I have been in.