Standing smelly water in outside waste water drain

Hi, Sounds like you'll need to excavate to see where the pipes go under the patio. Really you'd expect to see a drain head with a grill (a "hopper') at the patio surface level, into which the drain pipes release the water. The hopper would normally connect to a u-bend underground that maintains a reservoir of water inside to prevent foul smells returning upwards. Either that or a bottle trap assembly which does the same job. Recommend having a plumber (such as myself!) take a look - any decent plumber will know how to connect your waste to the correct drains in the correct way

feel free to reach out to us at ADM, this sounds like you have a blockage if the waste is going into a "gully pot" most likely there could be a blockage, You should be able to see the outlet. the smell will be from the stagnant water sitting in the gully/pipes.