Welcome BB, Ronald, we need more GD's , we hang out in GD's shed.
Nanny1, "O" ring, take the plug along to a specialist plumbers merchant ( not B&Q etc). they will have a selection of "O" rings and will fit a new one, shouldn't cost more than £1. Alternatively, if you know the size, they are available cheaply on eBay.
Ceiling joists - tap the ceiling with your knuckle or a piece of wood, the ceiling will sound hollow where there is no joist and solid where there is, marke the centre of the solid sounding area, this should be the centre of the joist. Do this across the ceiling and mark where you think the joists are. Measure the distance between your marks, they would normally be evenly spaced, if not repeat the process, with practice you will hear the difference in sound. To make sure, use a bradawl or small screwdriver to poke a small hole through the ceiling to check that you are hitting the joist, if you get it wrong, it is easy to fill the small hole.
OR -- spend £20 ish on an electronic device that will locate them for you, I have both, but find the knuckle tapping the easiest.
Crimson, tell your Daughter to start planting NOW, don't waste a season. You can sow Broad Bean Aquadulce Claudia until mid November, you will then get early crops in the late spring and the ground will be clear in time to plant summer crops. Aquadulce is the only hardy broad bean that can be sown now, do not try any other variety, the frost will kill them, Aquadulce will stand through the hardest frost. You can also plant Japanese onion sets or Shallots this month. I have planted both Broad Beans and Shallots this week.