how to work out where to put a downstairs toilet

Hi, installing a toilet under the stairs will be a bit tight but it's doable and handy to have that additional loo and basin. There are a couple of options that you can use, 1st option is to see if you can connect into an existing soil stack, you've got to make sure that there is a fall on the waste pipe. The 2nd option is to use a Saniflow or similar, the discharge pipe for a Saniflow can be 22mm and can be increased once outside the property but only if there is a fall towards the soil stack which is easier to run and connected into an existing soil stack only. Hope that helps and feel free to get in touch you require any more help. All the best