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View Full Version : What slope for waste pipes?



JK0
12-09-2011, 16:22 PM
When I moved into my present house six years ago, I had to install new drain connections for my washer dryer which is in my utility room.

The drain hose of my machine fits into a standpipe. This connects to a short length of 40mm pipe going through the wall, then into a 90 degree bend. From there there is a 90" length of pipe which drops around 6" until it joins a T-piece on the waste pipe connected to another standpipe in the kitchen. This ends about 3" above a gulley grid.

This has worked perfectly up to now. However, last night I noticed some spare underwear I kept in the cupboard next to the machine was going mouldy. At first I thought the hose had slipped out of the standpipe, so I pushed it back in.

This morning I found that the outside of the standpipe was wet after the spin cycle. Thinking there must be a blockage, I took apart the pipes and found barely anything.

I am stumped. Have I used too steep an angle for the 90" pipe? (I read somewhere it needs to be 1/4" per foot, but mine is about 3/4" per foot.)

tacpot
13-09-2011, 09:38 AM
Too steep is not a problem, too shallow is.

As there is no obvious blockage, I would replace the Washing Machine Trap with a sealed Appliance Trap (google "Appliance Trap") and use a blanking plug to blank off the unused waste.

JK0
13-09-2011, 18:39 PM
Thanks Tacpot.