I have a converted a part of a room to a small ensuite shower in a 1930s bungalow. The existing floorboards will be replaced with 18mm ply for tiling. The problem I have is that finished floor level is just a couple of inches above damp and the height of the path outside is just a couple of inches below damp. The groundworkers are going to put in a new gully outside for the shower and sink waste to run in to but I need to keep the waste pipe as high as possible as it leaves the property. The shower tray has a 50mm drain hole (70mm flange). I was thinking of using a standard shower trap such as code 47945; this will mean that the output is too low but then divert it up a little perhaps with a flexible hose such as Product Code: 86148. The top of the drain pipe will then be immediately beneath the bottom of the plywood floor then a Y into the sink waste with a about an inch of fall before it goes through the outside wall and into the gully. Is this OK? It would mean that the short piece of flexible hose would act a bit like a secondary trap (there would always be grey water in there).
flexi hose is the worst thing you could use, it wont act as a second trap but as an uphill run which will collect stagnant water and possibly cause backflow to the tray. As CGN says raise the tray, get a tray like the Mira Flight which has adjustable legs.
But I don't want to raise the tray. What is the problem with stagnant water downstream of the trap? And how can I get backflow to the tray when the highest parts of the waste fittings and pipe is below the tray?
From what you said in your first post and without actually seeing your set up it sounds as though you want to get water to go up hill at one point in your drainage. Even a slight incline could cause your tray to back up with waste water and at the very best be extremly slow to empty. The back fill will be caused by the fact that due to the waste not clearing as fast as it should it will struggle with the water coming from the shower and your feet will soon be in a few inches of water rather than as dry as they get in a shower. The theory of plumbing has evolved over many centuries but one of the first principles learnt is water wont go up hill.
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