DIY Doctor UK DIY Forums

We had a saniflow fitted with a shower, loo & basin in our loft. The company were not too reliable...

I need to know if its 'normal' for the shower tray to fill with waste water from the basin, when the tap runs in the basin?

Also, the shower tray empties very slowly... too slowly for the shower unless you run it on minimum flow (a power shower running from the hot water tank on the floor below)

We've had the saniflow serviced regularly as per manufacturers instructions. We had it's waste pipe replaced because it exited at a right angle and kept getting blocked... The new pipe has a curved bend & the saniflow has been fine since in this regard but I'm looking at having the plumbing redone to get better/right direction of waste...

Thanks - advice welcomed!

oh dear oh dear, lets start with physics. What empties water from anything is gravity and water will find the route of least resistance. It sounds like the plumber(cough cough) has teed the 40mm shower waste into the 32mm basin waste. When the basin is drained it's easier for the water to fill the larger shower drain pipe an fill the tray than it is to track down the smaller waste. The slow drainage of the tray could be an unsufficient fall (down slope) in the waste system or a reverse of the obove problem being that the tray is trying to run into a basin waste pipe(32mm). ALWAYS run an indipendant shower waste as far as the soil pipe. One answer is to fit a non return valve below the shower trap which will stop the basin water from entering the tray but it make the shower drain even slower.