I'm looking to install a drywell to handle some extra runoff from a patio. the patio is below the rest of the yard and a low point. it is graded to all go in one direction and I would like to put a long drain in that covers the 15 foot edge of the patio. i was thinking of a perforated pipe running the entire 15 foot edge and have that pipe covered with some blue river stones to mast the drain. this perforated pipe would attach to a drywell i plan to put in the ground. my question is do you think i would get smells coming back from the drywell up through the perforated pipe? i live in an area that would freeze and would not want to put in a trap if i don't have to. I would also like to use this drywell as a drain for an outdoor shower. there is no easy access to allow the outdoor shower to drain into any other garden beds or areas that need water. my only concern is that this shower would also require some form of trap and may possibly contain soaps (not many, but it is possible) that may linger in the drywell creating a possible smell.

fyi - plan for the shower would be a concrete pan under ground with a drain. above the pan would be the same blue river rocks that were used in the drain for the side of the patio.

please give me any advice or thoughts you may have.