Can I fit an Osma waste valve (http://www.screwfix.com/p/osma-waste-valve-white-x/3962k) after the shower trap to prevent back flow into the tray when either the basin is emptied or the toilet flushed? Will it cause any issues with the trap (syphoning or poor flow) or do I have to install it in place of the trap? As ever, any advice gratefully received. Willy.
1. Shouldn't cause any problems with existing trap, but its two points of failure instead of one. Replace the old trap with the one you suggest would be better, but see below. 2. There's something seriously wrong with the waste pipe-work for you to get backflow from either basin or toilet. It would be a much better long term solution to identify and rectify the problems. 3. As an easy first ste4p I'd suggest you see if there's a blockage in the soil pipe or between the soil pipe and the main sewer.
Hi Andy Thanks for the reply. I'll answer in reverse order - very eurovision... 3. Done that today as that was my first thought (and hope, as easiest to rectify) - removed the access cover and put camera into system - clean as a whistle in all directions (albeit slightly soiled). Client doesn't think that backflow has got any worse lately but isn't really sure - system is 14 years old and used very infrequently. 2. Agreed. There's an air admittance valve on the basin waste but no other venting that I can locate. It's a granny flat above a garage. The foul runs through the floor and along the underside of the garage ceiling before dropping away slightly to a septic tank approx 10m away - the ground slopes away so the flat is at ground level for the house/tank and the garage is lower. This is vented and there are two vented stacks in the house which the tank also serves. It's probably air pressure, rather than backflow I suspect, forcing the contents of the shower trap out when either the basin or toilet is used. 1. Good point thanks. Access under the shower tray is shocking - about 60-65mm between floor and tray base. There is a shallow trap (the builders had to scour some of the floor out to make it fit). All the pipework is solvent weld and runs around the 'front' of the tray obscuring both the trap and join between the 32mm basin waste and 40mm shower waste. This is directed through the floor into a strap on boss on the foul about 500mm downstream of the toilet. I think I will have to come up through the garage ceiling to make the alterations and extend the cement board boxing (which was installed around the foul) to cover up my access point. Thanks for your advice. Willy.
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