96 inches 8 foot high standpipe above floor passes manufacture specs on many machines. wont pass UPC but an example where I think it should is if there is a horizontal drain line say 3 foot or 5 foot off the floor what in the world would be so wrong with having a box up high the minimum stand pipe height and max imum might have reasons like suds or siponing the trap but the trap needing to be a certain distance off floor seems to have no sensible reason a trap 3 ft off floor with minimum stand pipe length should not be an issue. I cant say I understand all the thinking on codes or agree on UPC code in regards to this.
I think the heights for clothes washers are more "this is how we've always done it" than this is what works best. This is part of the code that came from screwed fittings and old pumps. My inspector did have a good point in that if the machine is changed and its pump isn't capable of that height, then the end user is hosed.. pun intended.
I didnt mention but agree with tuttles on the clean out as well , Ive allways felt it would collect stuff there i didnt really have knowledge it does but I have suspected it would but havent seen clean outs there very often. I just dont like it .
Combis on their backs without any fixture upstream will collect ... material behind them. The radius isn't sufficient to make everthing move completely downstream. And that is in any configuration, vertical or horizontal. Last summer we had a customer with a huge sag in their DWV system under the slab. We introduced a camera down the line and located the drain system with all the connection points so we could dig it up and fix it. At every combi connection to the horizontal main, whether vertical or horizontal, waste would flow both directions from the lateral... mostly in the direction of flow, but both ways nonetheless.
